A look-alike, double, or doppelgänger is a person who bears a strong physical resemblance to another person, excluding cases like twins and other instances of family resemblance.

Some look-alikes have been notable individuals in their own right, such as Britain's King George V and Russia's Tsar Nicholas II, who bore a striking resemblance to each other (they were first cousins). Other notable look-alikes have been notable solely for resembling well-known individuals, such as Clifton James, who acted as a double for British Field Marshal Bernard Montgomery during World War II.

Some look-alikes who have resembled celebrities have worked as entertainers, impersonating them on stage and screen, or at venues like parties and corporate functions. Professional look-alikes have often been represented by talent agencies specializing in celebrity impersonators.

Close physical resemblance between two or more individuals is also a common plot point in works of fiction.