So...you're getting yourself a new fur ball? That is great! But -- have you broken the news yet to your kitty yet? Chances are, kitty isn't going to share your enthusiasm - at least, not at first.
You see, cats are territorial by nature. They don't rely a pack or a group to back them up, so other cats are considered a potential danger; not a friend. Dumping one in their territory is likely to start world war III right there, in your living room. That said, with the right introductions, cats are perfectly capable of living in a group.
So, how do you introduce cats to each other?
Step 1: Create a safe haven
Set up the room - litter tray on one side, food bowl on the other, and the water bowl some distance away from the food bowl to prevent contamination. Put in a carton box to hide and sleep in. If it is an empty room, provide some objects, like furniture, to hide behind - your kitty will appreciate it. A scratching post by the door is excellent. And if you can, bring some familiar objects like a blanket with familiar smells, familiar food and familiar litter with you as you pick the cat up. A nice touch is to plug in a Feliway to make them as comfortable as possible.
Step 2: Bring your kitty home
When you go to pick up your new cat, don't forget to bring your cat carrier and be sure to ask anything familiar that you can bring with you - food, litter, blanket - to make the transition easier.
As you come home, go straight to the safe room - no letting the cats sniff each other just yet. And no introductions to the rest of the family, be it kids, dogs, rabbits or adults. It'll just cause undue stress and confusion. Once there, open the carrier, put the items you were able to bring with in the room, and leave. Yep. Leave. This cat has just been through a world of stress, and does not understand what is going on. What it needs is time to gain its bearings and check out the new environment - alone. If you want to keep an ear on things, feel free to stay in the room adjacent to kitty's, and give it about an hour. If you're dealing with a kitten, half an hour or even just 15 minutes should do the trick.
Open the door, and check up on the cat: is it out of the carrier? Is it hiding somewhere in the room? Has it found the litter tray? Is it rubbing up against your legs with its tail up? Has it eaten? Each one of these things will tell you at what stage of adjustment the cat is. You want to make sure that the cat eats within two days - normally, this isn't an issue - and you want to make sure that its litter box gets used. This too can take up to two days.
Most importantly, you do not want to move on to the next step, until the cat is eating and greeting you with its tail-up. Respect their (s)pace, while checking on them regularly. This may take a day or so.
Tip: Make sure your kitty has been cleared by a vet before physically introducing him or her to your other cat, and use this time as quarantine if he/she hasn't. A trip to the vet, after the cat has had time to acclimatise properly, is probably wise.
Step 3: I'm not alone...
Meanwhile, your other cat may have figured out that something is up. Let them check out the door to the new kitty if they want, while feeding them treats. Any good associations with the newcomer are definitely a plus.
Now, grab two small towels. Rub each cat gently down with a towel, from top to bottom with particular emphasis on the flanks and under and along the chin. Place the towel with the scent of your newcomer under the food bowl of your resident kitty and vice versa. This is an indirect introduction - cats can pick up a great deal from scents and pheromones about a stranger. The food bowl will act as a reward and positive association with the new smell.
As soon as you notice that both eat comfortably without hissing, crouching, or growling and are open to being petted while eating, you're ready for the next stage!
Tip: if you find that your resident kitty hisses at you after you've been in the room of the new kitty, it is because you have stranger danger all over you - in other words, you smell wrong.
To avoid this, use a bathrobe when you go into the new kitty's sanctuary, then disrobe once you come back out and wash your hands. This will avoid the encouragement of negative associations with the smell as well as feelings of confusion and animosity towards you.
Step 4: Who lives here?
So now we go on a field trip. Put your resident kitty in another small room or a pet carrier, placing them out of sight. Then open the door for the new cat. At their pace, let them investigate the entire house. Make sure the door to the safe room stays open so they can return there at all times. They may get overwhelmed at first and retreat a few times, but eventually you're hoping to see a tail-up while walking around and checking out the territory.
Once the cat no longer needs to retreat to the room, it's time to let the other cat investigate the safe room - close the door though, so they don't accidentally meet face-to-face. Supervise them as well, so they can indicate when they've had enough.
Then, return everyone to their corners to let things sink in.
Step 5: Peekaboo!
All right, time to stop pussy-footing around! Grab the food bowls of both cats and put them against the door, on each side. Or, alternatively, have someone feed the cat inside treats while you feed the cat outside treats. The point is - have them associate hearing and smelling the other cat with good stuff. Bribing is the way to go.
As soon as they are comfortable eating and more focused on the treats than on growling or hissing at what is behind the door, you're good to go.
Open the door just a little so nobody can pass through but they can see each other. There will be sniffing and perhaps some posturing which is normal. Keep it under 30 seconds though so there is little chance of escalation and close the door instantly if there is growling, hissing or meowing. Now rinse and repeat. Build up the amount of time that the door is open. If things escalate too much, close the door and try again an hour later, so everyone has time to cool down.
Once you're sure that there is no more posturing and everyone is relaxed, happy, tail-up and eating, you've succeeded in your mission.
And remember, if at any time things escalate, it means you've gone too fast and need to back up a step and start over.