A badge is a device or accessory, often containing the insignia of an organization, which is presented or displayed to indicate some feat of service, a special accomplishment, a symbol of authority granted by taking an oath (e.g., police and fire), a sign of legitimate employment or student status, or as a simple means of identification. They are also used in advertising, publicity, and for branding purposes. Police badges date back to medieval times when knights wore a coat of arms representing their allegiances and loyalty.

Badges can be made from metal, plastic, leather, textile, rubber, etc., and they are commonly attached to clothing, bags, footwear, vehicles, home electrical equipment, etc. Textile badges or patches can be either woven or embroidered, and can be attached by gluing, ironing-on, sewing or applique.

Badges have become highly collectable: in the UK, for example, the Badge Collectors' Circle has been in existence since 1980.

In the military, badges are used to denote the unit or arm to which the wearer belongs, and also qualifications received through military training, rank, etc. Similarly, youth organizations such as scouting and guiding use them to show group membership, awards and rank.