Buying a new puppy is an important decision, especially if you already own a dog. It may be a good idea to ask the previous owners or the pet store where you make your purchase how your puppy interacted with other dogs around him. If he didn't get along or if your other dog has acted aggressively to other dogs, you might have to spend a lot of time with them until they get accustomed to each other. When the day arrives to introduce your new puppy to your existing dog, you can give both dogs a .