What is the best bully stick for a large dog?

For large dogs 50–90 lbs, start with the 12 inch Standard bully stick. If they finish it in under 30 minutes, upgrade to the 12 inch Monster Jurassic (XL thickness) or the 12 inch Braided. Dogs over 90 lbs should go straight to the 12 inch Monster Jurassic or 12 inch Braided. Always size up when in doubt — a larger stick is safer than one that can be swallowed whole.

How many calories are in a bully stick?

A standard 6-inch bully stick contains approximately 80–95 calories. Researchers at Tufts Cummings School of Veterinary Medicine established approximately 88 calories as the average for a standard 6-inch stick. A 12-inch standard contains roughly 150–180 calories. Monster or XL thickness sticks run higher — approximately 110–135 calories for a 6-inch Monster and 200–260 calories for a 12-inch Monster. Always account for bully stick calories within the 10% daily treat rule.

What size bully stick should I get for my dog?

Match by weight: Under 20 lbs use a 4–5 inch Thin. 20–50 lbs use a 6 inch Standard. 50–90 lbs use a 12 inch Standard or 6 inch Monster. Over 90 lbs or aggressive chewers should use a 12 inch Monster Jurassic or 12 inch Braided. When in doubt, size up. A stick that is too large cannot be swallowed whole. A stick that is too small can become a choking hazard as it gets short.

Are bully sticks safe for puppies?

Yes, with the right size and supervision. Puppies with adult teeth, typically at 5–6 months, can safely have a 4–5 inch bully stick in 10–15 minute supervised sessions. Puppies under 5 months with baby teeth still erupting should not have bully sticks. Always supervise, always remove when the stick reaches 2 inches, and introduce slowly over the first week to let the digestive system adjust.

How long do bully sticks last?

For a moderate chewer: a 6 inch Standard lasts 25–50 minutes; a 12 inch Standard 45–90 minutes; a 12 inch Monster Jurassic 60–120 minutes; a 12 inch Braided 90–150 or more minutes. Aggressive chewers will finish any stick 30–50% faster. If your dog consistently finishes in under 15 minutes, size up to the next thickness tier or switch from straight to braided construction.

What age can puppies have bully sticks?

Puppies can have bully sticks once their adult teeth have erupted, typically at 5 to 6 months of age. Do not give bully sticks to puppies under 5 months or those still primarily on baby teeth — the hardness level can damage deciduous teeth. When in doubt, check with your vet to confirm adult teeth are established before starting.

What size bully stick is best for a puppy?

Start with a 4 to 5 inch Thin or 4 to 5 inch Braided Odor-Free for most puppies. The shorter length reduces leverage and makes it harder for puppies to bite off large chunks. Large breed puppies such as Labs, Goldens, and Shepherds at 6 or more months can move up to the 6 inch Standard. Never start a puppy on a 12-inch stick — the extra length creates too much leverage for a young chewer.

How long should a puppy chew a bully stick?

Start with 5-minute sessions in the first week, then extend to 10 to 15 minutes once the puppy has established confident chewing technique and shown no digestive upset. Maximum 20 minutes per session for puppies under 7 months. Always supervise the entire session and remove the stick when it reaches 2 to 3 inches regardless of how long the session has been.

Are bully sticks safe for teething puppies?

Bully sticks are safe for puppies with adult teeth coming in at 5 to 6 months, but not for very young teething puppies aged 2 to 4 months who are still on baby teeth. For early teething relief in puppies under 5 months, softer rubber chew toys or frozen options are more appropriate. Bully sticks become the right choice once adult teeth are established.

How often can puppies have bully sticks?

2 to 3 times per week is the standard recommendation for puppies. Daily use is fine once the puppy has adjusted to the treat after the first 2 to 3 weeks, but always account for the calories within the 10 percent daily treat rule. A 55 to 65 calorie stick represents a significant portion of a small puppy's daily intake — adjust meal portions on days bully sticks are given.

How much longer do braided bully sticks last than straight ones?

Braided bully sticks typically last 2 to 3 times longer than a straight stick of the same length for the same dog. The three-strand braided construction resists jaw compression better than a single strand, slowing consumption significantly. A dog that finishes a straight 6-inch stick in 15 minutes will often take 35 to 50 minutes on a braided 6-inch version.

Are braided bully sticks better for dental health?

Yes — braided construction provides better dental coverage than straight sticks. The ridges and valleys created by the braid contact teeth at multiple angles including the back molars where most tartar accumulates. A 2013 Rutgers University study found bully sticks reduced bacteria on dogs' teeth by 60.2%, and the braided format maximizes that benefit through extended contact time and multi-angle abrasion.

What size braided bully stick should I get for my dog?

Match by weight: Under 25 lbs use the 4 to 5 inch Braided Odor-Free. 15 to 40 lbs use the 5 to 6 inch Braided. 40 to 90 lbs use the 7 inch Braided Monster. 30 to 80 lbs focused on dental health use the 8 to 9 inch Braided. 50 or more lbs power chewers use the 12 inch Braided. When in doubt size up — a braided stick that is too large is always safer than one that can be swallowed whole.

Are braided bully sticks safe for puppies?

Yes — the 4 to 5 inch Braided Odor-Free is the recommended braided option for puppies 5 or more months with adult teeth. The braided construction is actually easier for puppies to grip than a straight stick. Always supervise, always remove at 2 to 3 inches, and limit sessions to 10 to 15 minutes for puppies under 7 months.

How many strands are in a braided bully stick?

Quality braided bully sticks use three strands of beef pizzle braided together. This three-strand construction creates the cross-laminated structure that resists jaw compression and delivers the 2 to 3 times duration advantage over straight sticks. Some lower-quality versions use two twisted strands — look for three-strand construction specifically when buying braided bully sticks.

Are odor-free bully sticks really odorless?

No bully stick is completely odorless. Odor-free means the strong, pungent smell of standard bully sticks has been significantly reduced through extended oven-baking that drives off the volatile organic compounds responsible for the strong odor. Most people find odor-free sticks barely noticeable indoors. Your dog will always be able to smell them — that is part of why they are so appealing.

How do odor-free bully sticks reduce smell without chemicals?

Legitimate odor-free bully sticks use extended high-temperature oven baking to drive off residual moisture and the volatile organic compounds that cause the strong smell. No chemicals, no liquid smoke, no bleaching. The result is the same single-ingredient beef pizzle with the same nutritional profile, just dried more thoroughly. Avoid any odor-free stick that lists smoke flavoring or has an unnaturally white color, as these indicate chemical processing or smell masking.

Do odor-free bully sticks have the same nutritional value as regular ones?

Yes. The extended baking process that reduces odor does not meaningfully change the protein content, fat content, or digestibility of the beef pizzle. Odor-free bully sticks retain approximately 86% crude protein and the same amino acid profile as standard sticks. Odor-free sticks are slightly drier, which is why they last marginally longer for many dogs.

Are odor-free bully sticks safe for puppies?

Yes — odor-free bully sticks are actually the recommended format for puppies because the reduced smell makes the introduction less overwhelming. The 4 to 5 inch Odor-Free or 4 to 5 inch Braided Odor-Free are the recommended starting sizes for puppies 5 or more months with adult teeth. Always supervise, limit sessions to 10 to 15 minutes, and remove at 2 to 3 inches.

Why do some bully sticks smell even when labeled odor-free?

Some brands label sticks as odor-free when they have simply added liquid smoke or other flavoring agents to mask the smell rather than reduce it through proper processing. Check the ingredients — genuine odor-free bully sticks contain only beef pizzle with no added flavoring. If you see smoke flavor, hickory smoked, or similar wording, the odor has not been reduced — it has been replaced.

What bully stick lasts the longest for aggressive chewers?

The 12 inch Braided bully stick consistently delivers the longest sessions for aggressive chewers — typically 90 to 150 minutes or more for power chewing breeds like Pit Bulls, Rottweilers, and German Shepherds. The three-strand braided construction at 12 inches provides maximum cross-laminated resistance. For extreme cases, the 32 to 36 inch Full-Length Cane provides 2 to 4 or more hours for giant breeds and extreme power chewers.

Are bully sticks safe for aggressive chewers?

Yes — bully sticks are one of the safest chews for aggressive chewers specifically because they are fully digestible. Unlike bones which can splinter, or rawhide which can cause blockages, bully sticks break down safely in the digestive system. Always supervise and remove when the stick reaches 2 to 3 inches — aggressive chewers are more likely to attempt to swallow the last piece whole, which is the primary choking risk.

What thickness bully stick do I need for an aggressive chewer?

Monster or Jurassic thickness minimum. Standard, Select, and Jumbo thickness tiers will not last adequately for true aggressive chewers. Look for explicit Monster, Jurassic, or XL thickness designations. For the highest resistance without braiding, the 12 inch Monster Jurassic XL thickness is the appropriate pick. For maximum resistance overall, move to braided construction.

How long should a bully stick last for an aggressive chewer?

A bully stick session should last at least 30 minutes for any aggressive chewer to provide meaningful behavioral benefit. The target range is 60 to 90 minutes. If current sticks last under 30 minutes, step up to Monster or Jurassic thickness or braided construction. If Monster Jurassic lasts under 45 minutes, move to the 12 inch Braided. If nothing hits 60 minutes, consider the 32 to 36 inch Full-Length Cane.

Can aggressive chewers have bully sticks every day?

Yes, with calorie management. A 12 inch Braided contains 240 to 300 calories and the 36 inch Cane contains 400 to 550 calories. For large dogs on daily bully sticks, reduce meal portions accordingly. The 10 percent treat rule applies — treats including bully sticks should not exceed 10 percent of daily caloric intake. For power chewing breeds with high energy output, daily bully sticks are generally fine with appropriate meal adjustment.

What is the longest lasting bully stick?

The 12 inch Braided is the longest lasting standard bully stick, delivering 90 to 150 or more minutes for most dogs 50 lbs and up. For giant breeds and extreme power chewers who finish the 12 inch Braided in under an hour, the 32 to 36 inch Full-Length Jumbo Cane delivers 2 to 4 or more hours. The 12 inch Braided is the right answer for most dogs — the 36 inch Cane is the escalation for exceptional cases.

How long does a bully stick last for the average dog?

For a moderate chewer in the 30 to 60 lb range: a standard 6-inch stick lasts approximately 25 to 50 minutes. A standard 12-inch lasts 45 to 90 minutes. A 12-inch Braided lasts 90 to 150 minutes. Actual duration varies by individual dog jaw strength, chewing style, and attention span. If your dog consistently finishes faster than these estimates, they are a heavy or aggressive chewer and should step up to the next thickness or construction tier.

Does a longer bully stick always last longer?

Not necessarily. For aggressive chewers, a denser shorter stick often outlasts a longer thinner one. A 6 inch Monster Jurassic at XL thickness lasts as long as a standard 12 inch for most medium-large dogs because the density difference outweighs the length difference. Length matters most for moderate chewers. For power chewers, always prioritize thickness and braided construction over length alone.

Why does my dog finish bully sticks so fast?

Your dog is most likely a moderate-to-aggressive chewer being given a standard-grade stick. Step up one tier in thickness: from Standard to Select, Select to Jumbo, Jumbo to Monster, or from straight to braided construction. If a 6 inch standard disappears in 10 minutes, try a 6 inch Monster Jurassic or a 6 inch Braided before buying a longer standard stick — density and construction will help more than length for aggressive chewers.

What is the best bully stick for keeping a dog occupied for 2 hours?

For most dogs 50 lbs and up, the 12 inch Braided consistently delivers 90 to 150 or more minutes. For dogs that need a guaranteed 2 or more hours, the 32 to 36 inch Full-Length Jumbo Cane is the only single bully stick format that reliably delivers that duration for dogs 80 lbs and up. The 12 inch Braided is the right starting pick — the 36 inch Cane is the escalation for extreme cases.

Can I Give a Bully Stick to a Dog That's Not Mine? Here's What to Know

Posted by Greg C. on Sep 11, 2026

Can I Give a Bully Stick to a Dog That's Not Mine? A Complete Safety Guide

Introduction

Giving a bully stick to a dog that's not yours is not something you should do without explicit owner permission and a thorough understanding of that dog's health history. Bully sticks are among the most popular dog chews available - single ingredient treats made from beef pizzle (bull penis) that are rich in high quality protein and fully digestible. But those same qualities that make them a healthy treat for one dog can create serious problems for another, especially when you don't know the animal's dietary restrictions, allergies, or chewing habits.

This guide covers every situation where you might consider offering a bully stick to someone else's dog: professional pet sitting, dog walking, visiting friends with dogs, and shelter or rescue volunteering. Whether you're a dedicated dog lover, a professional pet sitter, or a shelter volunteer, the stakes are real. Unauthorized treats can trigger allergic reactions, cause an upset stomach, create choking hazards, disrupt training protocols, and even expose you to legal liability.

The direct answer: Never give a dog a bully stick - or any treat - without first getting the pet owner's explicit permission and confirming the dog's dietary needs, allergies, and behavioral tendencies. When you don't have that information, skip the treat entirely.

By the end of this article, you'll understand:

Why owner permission is a non-negotiable first step before offering any treats
How to assess safety risks specific to bully sticks, including allergies, choking, and caloric concerns
Step-by-step protocols for professional pet care, social visits, and shelter volunteering
What alternatives to use when bully sticks aren't appropriate
The liability considerations that come with giving treats to dogs you don't own

Understanding When You Might Want to Give Treats to Other Dogs

The impulse to give a treat to a furry friend you don't own is natural. Dogs respond positively to food rewards, and offering a chew feels like an easy way to build trust or show affection. But the context in which you encounter another person's dog dramatically affects whether offering a bully stick is appropriate - and how much risk is involved.

Professional Pet Care Situations

Dog sitting and professional dog walking create a caregiving relationship where you're trusted with another pet parent's animal. Pet parents hire sitters and walkers with the expectation that their dog's diet, health, and safety protocols will be respected. In these roles, you may have some latitude to offer treats - but only within the boundaries the owner has clearly established.

The trust placed in professional pet care providers is significant. You're assuming temporary custody, which means decisions about treats, exercise, and feeding directly reflect on your reliability and professionalism. Giving a dog a bully stick that hasn't been specifically approved undermines that trust and could cause harm the owner didn't anticipate.

Social and Volunteer Situations

Visiting a friend's house, meeting a neighbor's dog at the park, or volunteering at an animal shelter are all situations where treat-giving feels casual but carries hidden complexity. At a friend's home, you might not know that their dog is on a limited-ingredient diet or has a beef allergy. At a shelter, animals often have unknown histories - their age, dental health, allergies, weight status, and disease history may be incomplete or entirely undocumented.

Treat-giving builds positive connections with dogs, but those connections shouldn't come at the expense of the animal's safety. Understanding why permission and safety checks matter is the essential next step before reaching for any chew.

Permission and Safety Assessment Requirements

Every risk associated with giving bully sticks to someone else's dog - from allergic reactions to choking to legal liability - can be managed or avoided entirely by following permission and safety protocols before offering a single treat.

Owner Permission Protocols

Always ask for explicit permission before offering any treats or dog chews to someone else's pet. This isn't just polite - it's essential. Your request should be specific: mention that you'd like to offer a bully stick (made from natural beef), and ask whether the dog has any dietary restrictions, food allergies, or treats that are off-limits.

Get clear guidelines on treat frequency and portion sizes. A 6-inch bully stick contains approximately 88 calories, and veterinary nutritionists recommend that treats and chews should not exceed roughly 10% of a dog's daily caloric intake. For a 50-lb dog with a daily energy requirement around 1,020 kcal, a single large bully stick could already push past that limit. Without knowing the dog's diet plan, you could easily overfeed.

High-value treats like bully sticks can also disrupt a dog's training protocols. If a pet owner is using specific treats for training reinforcement, introducing a different high-reward chew without their knowledge can undermine behavioral progress.

Health and Safety Considerations

When you don't know a dog's medical history, the potential risks of offering bully sticks multiply. Beef is one of the most common food allergens in dogs, alongside chicken, dairy, and lamb. Bully sticks can trigger severe digestive upset in dogs with food allergies - symptoms can include itching, ear infections, vomiting, and diarrhea. Some dogs have sensitive stomachs and may react poorly to bully sticks even without a diagnosed allergy.

Dogs on limited-ingredient or novel protein diets - often prescribed during allergy elimination trials - must avoid common proteins like beef entirely. Giving a bully stick to one of these dogs could invalidate weeks of careful dietary management. For dogs with known sensitivities, novel protein dog treats may be the only safe option, and that's a decision only the pet owner or their veterinarian should make.

Bully sticks should not be given to dogs with dietary restrictions without veterinary clearance.

Behavioral Assessment Factors

A dog's chewing habits and temperament are critical factors you may not be able to assess accurately if you don't know the animal well. Some dogs can become possessive of bully sticks, leading to resource guarding - growling, snapping, or biting when someone approaches during chewing. This behavior is more common with high-value chews and can be dangerous when the person nearby isn't familiar with the dog's triggers.

You also need to evaluate the dog's chewing style. Aggressive chewers may break off and swallow large pieces, increasing the risk of gastrointestinal blockage. Gentle chewers may take longer but still need supervision as the stick gets smaller. Bully sticks should match a dog's size and chewing style - select thinner sticks for small dogs and thicker for larger breeds. Without knowing whether the dog enjoys bully sticks or has had them before, you're introducing a new chew with unpredictable results.

Key safety assessment points:

Confirm no beef allergy or protein sensitivity
Verify the dog is not on a restricted or elimination diet
Assess chewing style (aggressive vs. moderate)
Check for resource guarding history
Choose the appropriate size bully stick for the dog's size
Plan for active supervision throughout chew time

These assessments form the foundation for the specific protocols you'll follow depending on your situation.

Step-by-Step Protocols for Different Scenarios

With permission secured and safety factors assessed, the specific steps you follow depend on your relationship with the dog and its owner. Professional settings demand documentation; casual encounters require good judgment; shelter environments require strict adherence to organizational rules.

Professional Pet Sitting Protocol

Professional pet care carries the highest level of responsibility and the greatest need for formal protocols.

Discuss treat preferences during the initial client meeting. Ask about approved treats, brand preferences, and whether the owner uses high quality bully sticks or other natural dog chews. Clarify if the dog has experience with bully sticks specifically.
Document approved treats and feeding instructions in writing. Include protein types allowed, portion sizes, frequency limits, and any foods that are strictly prohibited. Written documentation protects both you and the pet parent.
Confirm emergency vet contact information and establish protocols for treat-related incidents - what to do if the dog shows signs of choking, an allergic reaction, or digestive issues.
Follow the owner's supervision and timing guidelines exactly. If the owner says to limit chew time to 15 minutes, set a timer. Remove small pieces of bully sticks to prevent choking hazards. Use a bully stick holder to keep the last inch secure and prevent the dog from attempting to swallow large pieces.

Puppies can have bully sticks after six months old, but require extra caution. Choose thinner bully sticks for puppies to prevent injury, supervise puppies while chewing bully sticks to prevent choking, and limit chew time to 10–15 minutes for puppies with bully sticks. Bully sticks can cause dental fractures in puppies if too hard - this is information the owner should confirm before you offer one.

Social Visits and Casual Interactions

Casual settings require less documentation but no less caution.

Ask the host's permission before offering any treats to their dog. Be specific about what you'd like to give - saying "Can I give your dog a bully stick?" is better than "Can I give your dog a treat?"
Respect "no treats" policies without taking offense. Pet owners may have reasons - dietary restrictions, weight management, behavioral training - that they don't feel obligated to explain.
Offer to bring owner-approved treats for future visits. This shows respect for the owner's preferences while maintaining your ability to bond with their pup.
Focus on non-food bonding activities if treats are declined. Play, petting, interactive toys, and puzzle feeders all provide mental stimulation without the risks associated with food treats.

Shelter and Rescue Volunteering

Animals in shelters often have unknown health histories, making unauthorized treat-giving especially risky. Follow facility protocols without exception. Most shelters maintain approved treat lists and specific distribution procedures. Never bring outside treats - including bully sticks - without explicit staff approval. Microbial contamination is a particular concern in shelter environments: studies have found that approximately 4% of bully stick samples tested positive for Clostridium difficile, and MRSA has also been isolated in some samples. Immunocompromised animals in shelters are especially vulnerable to harmful bacteria.

Protocol Step	Professional Pet Sitting	Social Visits	Shelter Volunteering
Permission Required	Written client approval	Verbal host permission	Staff/organization approval
Documentation	Client instruction sheet	Mental note/conversation	Facility feeding protocols
Supervision Level	Follow owner guidelines	Host determines	Facility requirements
Liability	Professional insurance	Personal responsibility	Organization coverage

Choose your protocol based on the formality of your relationship with the dog and its owner. In every scenario, the underlying principle is the same: you need permission, you need information, and you need to supervise.

Common Challenges and Solutions

Following proper protocols is straightforward in theory but can feel awkward or limiting in practice. Here's how to handle the most common obstacles.

Owner Says "No" to Treats

Respect the decision completely. Many pet parents have carefully calibrated their dog's diet and don't want outside interference. Instead, bond with the dog through play, walks, or simply calm companionship. Ask whether there are specific owner-approved treats you could bring on future visits - this shows you care while respecting boundaries.

Dog Has Dietary Restrictions

Work directly with the owner to identify suitable alternatives. If the dog has a beef allergy, bully sticks are off the table entirely. Alternative chews made from novel proteins - such as buffalo, venison, or lamb - may be options, but only with the owner's approval. Non-food enrichment activities like chew toys, puzzle feeders, and interactive games can provide mental stimulation and satisfy chewing instincts without any dietary risk.

Uncertainty About Dog's Health History

When you don't have reliable information about a dog's health, default to a strict "no treats" policy. This is especially important with bully sticks, which carry potential risks related to allergies, caloric load, and choking. Unlike rawhide, bully sticks are 100% digestible within hours and do not splinter like bones - making them a safer alternative in many respects - but "safer" does not mean "safe without context." Focus on interaction methods that don't involve food rewards until you can confirm the dog's dietary profile.

Emergency or Unexpected Situations

If you're caring for someone's dog and an unexpected situation arises - the dog is anxious, destructive, or stressed - contact the owner before reaching for treats. Bully sticks provide mental stimulation and can calm anxious dogs, but introducing a new treat during a stressful moment adds unpredictability. Chewing a bully stick can lead to intestinal blockage if swallowed whole, and a stressed dog may chew more aggressively than usual. Prioritize safety over treat-giving in all unexpected circumstances.

Conclusion and Next Steps

Giving a bully stick to a dog that's not yours is a decision that requires more thought than most people realize. Bully sticks are generally safe, nutritious, and beneficial - they are rich in protein and essential nutrients, promote dental health by reducing plaque buildup, and support healthy teeth through natural chewing action. Bully sticks are made from a single ingredient: beef pizzle, with no artificial ingredients or chemical treatments. But those nutritional benefits only matter when the treat is appropriate for that specific dog, given with the owner's knowledge, and supervised properly.

Here are your immediate action steps:

Always ask explicit permission from the dog's owner before offering any treats - be specific about the type of chew
Assess the dog's health history and dietary restrictions thoroughly before selecting any treat
Follow the proper protocol based on your situation - professional, social, or volunteer
Supervise every chew session and remove the bully stick once it's chewed down to the last inch to prevent choking
Choose alternative bonding activities when treats aren't appropriate or when health information is unavailable

If you're looking to learn more about choosing safe bully sticks for your own dog, understanding how bully sticks fit into a dog's diet, or exploring why dogs enjoy them so much, those are worthwhile next steps. When you feel confident about bully stick safety for your own pet, you'll also be better equipped to have informed conversations with other pet owners about whether their dog can enjoy one too.

Additional Resources

For professional pet sitters: Create a standardized client intake form that covers approved treats, dietary restrictions, allergies, emergency contacts, and supervision preferences. Look for bully sticks made from natural, high-quality beef - opt for odor free options for indoor use, and store bully sticks in an airtight container in a cool, dry place with proper storage to maintain freshness.
Alternative bonding activities: Interactive puzzle feeders, tug toys, fetch, gentle grooming, and calm companionship all build positive relationships with dogs without introducing dietary unknowns.
Common allergy signs: If a dog shows itching, ear infections, vomiting, or diarrhea after any new treat, discontinue immediately and inform the owner. Beef is among the most common food allergens in dogs - awareness helps you respond quickly.
Puppy-specific guidelines: Puppies require age-appropriate sizing, shorter chew sessions, and closer supervision. Bully sticks can cause dental fractures in puppies if the stick is too hard or too thick for their developing teeth.
Legal awareness: In many U.S. states, someone who temporarily assumes care, custody, or control of a dog may bear legal responsibility for incidents during that period. Strict liability statutes regarding dog bites can apply if a dog becomes aggressive while guarding a high-value treat you provided.

Can I Give a Bully Stick to a Dog That's Not Mine? Here's What to Know

Can I Give a Bully Stick to a Dog That's Not Mine? A Complete Safety Guide

Introduction