I've just brought home a new kitten, my cat is hissing at her

There are a few simple rules to help cats live together peacefully: - Set up multiple feeding stations so they aren't forced to share food, which is often a source of conflict for cats. - If you have two cats, you need three litter trays in different locations to avoid territorial issues. You can always remove one later once they’ve each settled on their own. - Provide plenty of spots where they can go to be alone and sleep in peace. Who knows, they might even end up sleeping together one day! - Don't "force" them to accept one another; let things happen at their own pace. - Your first cat will undoubtedly be a bit bossy with the kitten at first, just to show him the ropes and establish the house rules. Whatever you do, don't tell him off. Instead, separate him from the kitten with a firm but non-aggressive "NO", then reassure him of your affection. - To begin with, never leave them alone together unsupervised – you just never know. - You could also try plugging in a Feliway diffuser, which can really help. Finally, I’d say trust the kitten's ability to get itself accepted. They might never be "thick as thieves" as the saying goes, but as long as you make sure everyone has their own space, it should be fine. Every kitty has their own personality, so make sure you’re meeting their individual needs, which won't necessarily be the same. Good luck and keep us posted on how they're getting on!