A custom motorcycle is a motorcycle with stylistic and/or structural changes to the 'standard' mass-produced machine offered by major manufacturers. Custom motorcycles might be unique, or built in limited quantities. While individual motorcyclists have altered the appearance of their machines since the first days of motorcycling, the first individualized motorcycles specifically labeled 'Custom' appeared in the late 1950s, around the same time as the term was applied to custom cars.

A custom car is a passenger vehicle that has been altered to either improve its performance, change its aesthetics, or a combination of both. Some automotive enthusiasts in the United States want to push "styling and performance a step beyond the showroom floor - to truly craft an automobile of one's own." A custom car in British according to Collins English Dictionary is built to the buyer's own specifications.