Costume design is the fabrication of apparel for the overall appearance of a character or performer. This usually involves researching, designing and building the actual items from conception. Costumes may be for a theater or cinema performance but may not be limited to such. Costume design should not be confused with costume coordination which merely involves altering existing clothing, although both create stage clothes.

Four types of costumes are used in theatrical design, Historical, fantastic, dance, and modern.

Designs are first sketched out and approved, then either draped on a form or a pattern drafted. Along with the fabricated portion, the costume may require accessories such as footwear, hats and head dresses for the actors to wear, but it may also include designing masks, makeup, wigs, underwear or other unusual specialty items, such as the full body animal suits for the characters in the musical Cats (designed by John Napier, winner of the 1983 Tony Award for Best Costume Design). Costumes budgets will generally be as high a cost as other departments or theatrical needs such as set design.