Płock [pwɔt​͡sk] ( listen) is a city in central Poland, on the Vistula river. According to the data provided by GUS on 30 June 2009 there were 126,675 inhabitants. It is located in the Masovian Voivodeship (since 1999), having previously been the capital of the Płock Voivodeship (1975–1998). It now is a capital of a Powiat (county) at the extreme west of the Mazovian Voivodeship. In years: 1079 - 1138 Płock was capital of Poland. Płock is also a historical capital of Mazovia.

Płock was the capital city of Poland during the reign of the Polish monarchs Władysław I Herman and Bolesław III Krzywousty (1079–1138). It was also a seat of several of the Dukes of Masovia and one of the capitals of that state.

During the German occupation of Poland (1941 to 1945) it was named Schröttersburg, after the former Prussian Upper President Friedrich Leopold von Schrötter.

The Duke Capital City of Płock (Polish: Stołeczne Książęce Miasto Płock) is the official title of Płock used in ceremonial documents and for preserving traditions. It is the formal legal title included in the preamble to the City Statute of Płock. The title is a result of the fact that from 1079–1138 Płock was the capital of Poland. It performed this function during the reign of the Polish monarchs Władysław I Herman and Bolesław III Krzywousty.