Introducing a new pet into your home can be a bit of a challenge. This is especially true if there are current resident pets already in your household. Resident pets often times are very territorial and may become jealous of the new family member causing unwanted reactions from both sides. To help assure that both new and resident pets are properly socialized, and that they are able to cohabitate with each other, there are some techniques that you should follow. With a bit of caution and patience you will ease the transition and develop a safe happy household for both pets.

When first introducing a new dog to a resident dog, pick a location that is not familiar to either animal. This will prevent your resident dog from viewing the newcomer as an intruder invading their territory. Leash both dogs and have a separate person handle each. Having another person handle the other makes it easier to restrain the dogs should you need to separate them.

Before bringing them close enough for physical contact, allow your pets to know of each other's presence. Enforce good feelings by offering your pets a treat as well as petting them. This will associate and establish each other's presence with positive feelings.
Leash both dogs and have a separate person handle them each.
Associate good feelings with the presence of another pet using treats.

Eventually you'll want to get your pets close enough so they can greet each other. Your dogs will sniff each other (this is normal canine greeting behavior). While they are sniffing each other, speak to them in a friendly tone and reward them with positive reinforcement. Don't let them sniff each other for too long though as one can take it as an annoyance and respond with aggression.

Use a toy such as the Bettie as a diversion should aggression escalate between the two pets.

Your pets might not take to liking each other right away.  If you notice that either dog is getting too aggressive immediately interrupt their interaction and get each dog interested in something else. Toys or treats will provide a great distraction, allowing you to separate the two dogs.

After the aggression has regressed, you can try to introduce them again in short intervals. If you have more than one resident dog, introduce them to your new dog one at a time. This will prevent them from ganging up on the newcomer.
If you are introducing a puppy to an adult resident dog, it is important to never leave them alone until you are certain that they are not in any danger. Younger puppies may not recognize the cues adult dogs signal when they are annoyed. Most well socialized adult dogs will give puppies a warning snarl or growl- this is perfectly normal. Those that are not well socialized will respond to a puppy with more aggressive behavior such as biting which can harm the puppy.

There is a lot of prep work you should do before letting your new cat free to roam around along with your other cats. Cats are very territorial and some are more social than others.  Initially, the best way to introduce cats to each other is to keep them apart.

Keep your new cat separated from the other cats in a medium sized room with their litter box, food, water, and a bed. You can slowly introduce your cats to each other's presence by feeding them close to the door that separates them. This will allow your cats to investigate each other's unique scents and smells without direct contact or seeing each other. Eventually you will want to open the door just enough so that they can see each other without being able to get too close for physical contact.
Place food bowls such as our favorite Lucy food bowl on opposite sides of the door that seperates your cats to feed them.

After a few days you will want to switch the cat's environments so that they can further investigate each other's scents before finally letting them roam freely. When your new cat is exploring their new environment, it will make them less susceptible to being frightened.

The use of Feliway will bring out the best behavior in both cats. Feliway is a natural treatment that mimics a cat's pheromones so that they are prevented from spraying or clawing. Feliway will also calm your cats in stressfully situations. Once you are certain that your cats can at least tolerate each other you can engage a less social cat with the use of a catnip such as Krazy Kitty Katnip.

One of the keys to successfully socializing your cat and dog is to introduce them to each other while they are young. Puppies and kittens that play nice at a younger age are more than likely to grow up to be adult dogs and cats that get along. It is important that you do not leave your pets alone together until you are certain they are properly socialized. Always keep your new pets supervised.

Start off by having your pets be familiar with their new environment. Besides physical space, this also includes having your pets get familiar with each others sounds and scents. You can introduce your new pet to your other pet's items such as their beds and blankets. Slowly introduce your new puppy to your cat by letting them be aware of each other's presence without any physical contact. This will entail restraining your puppy and allowing the cat to explore their new friend. It's important to keep your cat safe. Though cat's can attack and fend for themself, dogs, even puppies, are more likely to deal the most physical harm.

Should your puppy get overly excited by your cat's presence, give a prompt "no" command and give them a chew toy to play with. This will teach your puppy that it is not okay to go after your cat and that biting and chewing with their own toys is acceptable.

The use of TranQuil-Tabs for dogs may calm puppies and dogs that get overly excited when introduced to your pet cat.
Familiarize your new pet with your other pet's scents by introducing them to your other pet's beds. This Otis and Claude Sleep Bed is ideal for cats and small dogs.
Teach your pet puppy that chewing on their toys is acceptable and attempting to chew on the cat is not. Premier offers a variety of durable chew toys like the Squeez Meeze Lady Bug above.
Always keep an eye out for both pets and never leave them alone with each other unless you are certain that they will not cause each other physical harm.