Proof of concept, also known as proof of principle, is a realization of a certain idea, method or principle in order to demonstrate its feasibility, or viability, or a demonstration in principle with the aim of verifying that some concept or theory has practical potential. A proof of concept is usually small and may or may not be complete.

A concept car is a car made to showcase new styling or new technology. Concept cars are often exhibited at motor shows to gauge customer reaction to new and radical designs which may or may not be mass-produced. General Motors designer Harley Earl is generally credited with inventing the concept car, and did much to popularize it through its traveling Motorama shows of the 1950s.