The (First) Castilian Civil War lasts three years from 1366 to 1369.

It becomes part of the larger conflict then raging between the Kingdom of England and the Kingdom of France: the Hundred Years' War.

It is fought primarily in the Kingdom of Castile and its coastal waters between the local and allied forces of the reigning king, Peter, and his illegitimate brother Henry of Trastámara over the right to the crown.