The Four Days' Battle was a naval engagement fought from 11 to 14 June 1666 during the Second Anglo-Dutch War. It began off the Flemish coast and ended near the English coast, and remains one of the longest naval battles in history.

The Second Anglo-Dutch War, or Second Dutch War, began on 4 March 1665, and concluded with the signing of the Treaty of Breda on 31 July 1667. One in a series of naval conflicts between England and the Dutch Republic, its causes were a combination of political differences and commercial disputes.