If this is a new behavior for your cat, take him to your vet to rule out the possibility that he may have a urinary tract infection. Otherwise, take a step-by-step approach to get him to use the litter box. You can start by keeping him in a small area, such as a bathroom, where he has food and water as well as his litter box. Once he's successfully using his litter box, slowly increase the amount of space he's allowed, but be sure to go back a step and repeat the process if any accidents occur. For more tips and advice, read our article on Litterbox Training.