When it is time to introduce a new cat to your home, all parties involved will need to learn to make changes for cat health and cat safety. For people this will not be too difficult, however the existing cat and the new cat are who we need to focus on. Though cats are generally solitary in the wild, they are typically able to adapt to new family members if done correctly. The territorial nature will be the main issue, so you should proceed slowly and attentively when introducing cats to each other.

When dealing with kittens, it will not take so much time, maybe a week or so. Kittens are more amenable to change, while an older cat might not be. The attitudes and personalities are huge factors. You must take care to give love and affection to existing cats, so they will not feel usurped by the new cat. Keep the newcomer in a separate room to kick off the introduction. An unused bathroom or bedroom with bed, water, food, litter box, toys, and a repeated human visitor to play with will be necessary. The existing cat will be denied entry here, so the new cat can be comfortable and feel protected.

Certainly, the new cat will be concerted, since the existing cat will yowl and hiss through the door. This is a message that the house is already the property of a cat. Let them go on, because they need to get that out of their system before they can start accepting the newcomer. Eventually they'll stop that. Their scents will pass under the door, and possibly paws as well. When the resident cat calms down praise them for their restraint.

Next you start them using the same food dish, further intermixing their scents. Don't feed them together yet, though you will be using the same dish for both cats. Inexorably they will get become accustomed to the unusual smells and the danger is lessened.

After, you release them in the house together for increasing time frames. Hissing and dominance games will ensure, but do not allow actual fighting. This is the time for playing with them together and sharing. Extend the lengths of time, but the new cat will need to go in the protected room for some of the time as well, to calm them and all parties need their individual time with the parent figure.

It does not usually happen immediately, but after a while you can leave them unsupervised. They may not yet be close, but acquiescence to the fait accompli is the crucial task. It's all a question of time from there on out. With the territorial concerns resolved (and that includes jurisdiction over the humans, too!) your cats will work on being lifelong pals and happy healthy cats.