A litter box, also known as a sandbox, cat box, litter tray, cat pan, potty, pot or litter pan, is an indoor feces and urine collection box for cats, as well as rabbits, ferrets, miniature pigs, small dogs, and other pets that instinctively or through training will make use of such a repository. They are provided for pets that are permitted free roam of a home but who cannot or do not always go outside to excrete their metabolic waste.

In the wild, cats naturally excrete in soft or sandy soil for easy burial. They use their paws in a backward sweeping motion to cover their feces. To stimulate this instinctive desire, a litter box's bottom is typically filled with 2 inches (5 cm) or less of cat litter. Litter box filler is a loose, granular material that absorbs moisture and odors such as ammonia. Some litter brands contain baking soda to absorb such odors, or owners may sprinkle a thin layer in the bottom of the box, under the cat litter. The litter material also satisfies a cat's instinctive desire to hide their scent by allowing them to bury their waste. The most common material is clay, although recycled paper "pellets" and silica-based "crystal" variants are also used. Sometimes, when an owner wishes to stimulate the cat's natural instincts, natural dirt is used.

The litter can give off a strong odor, and must be disposed of periodically. It is recommended that the litter box be kept in low traffic areas of the home, such as a basement or laundry room to avoid litter box aversion. There are commercially available special types of litter to help cover or lessen the odor produced. They contain baking soda, plant extracts and/or odorized crystals. If kept in a room with an intake vent, an air freshener may be added on the furnace filter to isolate the odor from the rest of the house.