A folk costume (also regional costume, national costume, traditional garment, or traditional regalia) expresses an identity through costume, which is usually associated with a geographic area or a period of time in history. It can also indicate social, marital or religious status. If the costume is used to represent the culture or identity of a specific ethnic group, it is usually known as ethnic costume (also ethnic dress, ethnic wear, ethnic clothing, traditional ethnic wear or traditional ethnic garment). Such costumes often come in two forms: one for everyday occasions, the other for traditional festivals and formal wear. The word "costume" in this context is sometimes considered pejorative due to the multiple senses of the word, and in such cases "regalia" can be substituted without offense.

Following the rise of romantic nationalism, the pre-industrial peasantry of Europe came to serve as models for all that appeared genuine and desirable. Their garments are crystallized into so-called "typical" forms, and enthusiasts adopted that attire as part of their symbolism. These garments may be made from traditional pre-industrial textiles, in regional styles.

In areas where Western dress codes have become usual, traditional garments are often worn at special events or celebrations; particularly those connected with cultural traditions, heritage or pride. International events may cater for non-Western attendees with a compound dress code such as "business suit or national dress".

In modern times, there are instances where traditional garments are required by sumptuary laws. In Bhutan, the traditional Tibetan-style clothing of gho and kera for men, and kira and toego for women, must be worn by all citizens, including those not of Tibetan heritage. In Saudi Arabia, women are also required to wear the abaya in public.