The Treaty of Dover, also known as the Secret Treaty of Dover, was a treaty between England and France signed at Dover on 1 June 1670. It required that Charles II of England would convert to the Roman Catholic Church at some future date and that he would assist Louis XIV with 60 warships and 4,000 soldiers to help in France's war of conquest against the Dutch Republic. In exchange, Charles would secretly receive a yearly pension of £230,000, as well as an extra sum of money when Charles informed the English people of his conversion, and France would send 6,000 French troops if there was ever a rebellion against Charles in England. The secret treaty was signed by Arlington, Arundell, Clifford, and Bellings for England and Colbert de Croissy for France. The two kings exchanged letters of ratification and kept secret the existence of the treaty. A public treaty of Dover was also negotiated, but it was a screen designed for propaganda purposes and to hide the religious dimension of the secret treaty. The Third Anglo-Dutch War was a direct consequence of this treaty. The actual treaty was published by historians a century later.

Dover () is a town and major ferry port in Kent, South East England. It faces France across the Strait of Dover, the narrowest part of the English Channel at 33 kilometres (21 mi) from Cap Gris Nez in France. It lies south-east of Canterbury and east of Maidstone. The town is the administrative centre of the Dover District and home of the Port of Dover.

Archaeological finds have revealed that the area has always been a focus for peoples entering and leaving Britain. The name derives from the River Dour that flows through it.

In recent times the town has undergone transformations with a high-speed rail link to London, new retail in town with St James' area opened in 2018, and a revamped promenade and beachfront. This followed in 2019, with a new 500m Pier to the west of the Harbour, and new Marina unveiled as part of a £330m investment in the area. It has also been a point of destination for many illegal migrant crossings during the English channel migrant crisis.

The Port of Dover provides much of the town's employment, as does tourism including to the landmark White Cliffs of Dover. There were over 368,000 tourists visiting Dover castle in the year of 2019.