Arthur I (29 March 1187 – probably 1203) is Duke of Brittany between 1194 and 1202.

He is the posthumous son of Geoffrey II, Duke of Brittany and Constance, Duchess of Brittany.

As Geoffrey's son and heir he also is Earl of Richmond.

Geoffrey is a son of Henry II of England, younger than Richard I but older than John.

In 1190, Arthur is designated heir to the throne of England and its French territory by Richard I, the intent being that Arthur would succeed Richard in preference to Richard's younger brother John.

Nothing is recorded of Arthur after his incarceration in Rouen Castle in 1203, and his precise fate is unknown.