*Information adapted from Best Friends Animal Society*
If you know that both dogs are social with a variety of other dogs, the meeting should be easy. However, some dogs haven't been around many other dogs, so the introduction may require more caution and effort. Another consideration is whether the dogs have been spayed or neutered. If they haven't, the meeting could be more difficult. If either dog has previously had difficulty getting along with other dogs, consider a certified professional behavioral consultant to help with gradual introductions.
Have the dogs meet on neutral ground — somewhere outside of the home so they're not likely to feel territorial. If you're adopting from a shelter, ask the staff if they can help to introduce the dogs. A pet supply store trainer could also help. Keep each dog on a loose leash and walk them side-by-side with a safe distance between them. Then, cross paths while still maintaining the distance and allow the dogs to smell where the other has walked. Avoid nose-to-nose greetings, as this can be stressful for dogs. Be sure to remain calm throughout the meeting. If either dog barks, snaps or lunges at the other, consider a certified professional behavioral consultant.
Next, let the dogs approach each other. Watch their body language closely, paying attention to the entire body. If you're unfamiliar with dog body language, have someone there who is familiar with it. If the dogs seem comfortable with each other, take them to an enclosed area, drop the leashes and give them space to get to know each other. If one dog is overbearing and the other isn't correcting them, you can say something like "Hey, knock it off!" But if they are engaging in a polite, appropriate manner, you can say something like "Good!" in a happy tone. Only physically separate the dogs if they're getting too excited and can't calm down or if it looks like they're heading for conflict.
Body language to watch
If the dogs stiffen and stare at each other with their hair up and teeth bared, they probably won't become fast friends. If they lunge at each other and try to fight, separate them and don't try any more introductions without help from a certified professional behavioral consultant. Some dogs may be able to ignore other animals in public, but can't safely interact with them and would live best as an only pet.
If the dogs rush up to each other — with or without their hair raised — and engage in loud, rowdy play, stay alert. This could escalate into a fight if they don't know how to calm down.
If one dog continually pursues the other and ignores the other dog’s corrections, this can turn into bullying. Corrections, such as curling their lip, growling or snapping at the air, are part of normal and healthy dog communication. Dogs should be able to give and accept corrections from other dogs. It's also important for them to take turns chasing and being chased, and to take breaks when they get too excited. If they can't do that, pick up their leash and walk them around until they relax.
If the dogs try to paw at each other or play bow, they may want to be friends. Allow them to get to know each other, and praise positive interactions.
Bringing the new dog home
If the dogs seem fine with each other, drive them home, preferably in separate crates. At home, put away the first dog's food bowls, toys, bones and other items that could cause conflict. When you feed the dogs or offer treats or bones, separate them while they eat. Once they become more familiar with each other, they may be more willing to eat together.
If the newcomer is a puppy, the two may need frequent breaks from each other. Some adult dogs lose patience with puppy energy. If the dog doesn't like the puppy, don't leave them alone together.
Remember, if you're uncomfortable at any point, seek help from a certified professional behavioral consultant.