Some cats are more vocal than others, but if your cat won't stop meowing — especially if this is new behavior — it's worth looking into. Cats have many weird behaviors that are innocuous, but when your cat won't stop meowing excessively, it could mean he needs something from you, or possibly that he is in pain.
Meowing for food
It probably comes as no surprise that cats sometimes meow when they're hungry. To some degree, this behavior is normal; your cat might meow a moderate amount while you're opening up his food can. (Mine certainly does.) However, if he suddenly starts meowing considerably more at mealtime, or throughout the day, take him to the vet to make sure something hasn't changed with their health.
Crying for attention
Another unsurprising reason your cat might be meowing is for attention. If your cat is bored or lonely, he might meow so you pay attention to him. If this happens, don't give in when he meows, but rather provide more entertainment throughout the day. Buy or make him some stimulating toys, and make sure you dedicate time every day to playing with him.
Stress and anxiety
Stressed cats are likely to voice their stress loudly. Has a big change recently come into your (and your cat's) life, such as a new baby or a new pet? Cats are sensitive to change and can become stressed in new situations. If you suspect that your cat is stressed because of a recent change, give him lots of love, attention, and quiet one-on-one time to help ease their anxiety.
Pain or aging
A cat that's meowing excessively might be in pain. It's always a good idea to take your cat to the vet first to rule out this possibility.
Just like people, cats can experience confusion as they age. If an older cat won't stop meowing, take him to the vet. Vets can prescribe medications that help cats suffering from confusion or disorientation. Vision and hearing loss may also cause your cat to meow more often.
Desire to breed
If your cat isn't fixed, a female may yowl when she is in heat and a male may yowl when he smells a female in heat. Yowling is one way cats try to attract a mate.
If your cat isn't fixed, take him to the vet to get fixed as soon as possible. Spaying your female cat will prevent her from going into heat and should stop this behavior. Neutering male cats can also stop unwanted behaviors such as yowling and marking.
Cat won't stop meowing considerations
Always take your cat to the vet when there's a marked change in behavior, like sudden excessive meowing. The vet will be able to rule out possibilities like illness and disorientation and will help get you on the road to curing what ails your kitty.
Don't punish your cat for meowing. It won't work, and it will make your cat distrust you. Don't give in, either. If you have ruled out medical conditions and your cat is meowing for food or attention and he receives it from you, he will learn that this technique works, and then you'll be trapped in a cycle of meowing for the rest of your life together.
When in doubt, always check with your vet first, and show your cat lots of love and patience.