Pisz is a town in the Warmia-Masurian Voivodship in Poland. With a population of 19,328 (2004) , it is the seat of Powiat Piski. Pisz is located at the junction of Lake Roś and the Pisa River.

The site of Pisz was originally inhabited by the Old Prussians. In 1345 the Teutonic Order began constructing a castle nearby at the southermost point of the Piska Forest in the Masurian Lakeland. The castle was named Johannisburg, after St. John the Baptist. The settlement nearby held a market as early as 1367, but it was not until 1645 that it received its town charter. The German-speaking residents of the town referred to it as Johannisburg, while the Polish-speaking residents referred to it as Jańsbork. Its early growth owed much to the residents’ skill in beekeeping, and it was located on trade routes leading to Gdańsk and to the Vistula and Narew rivers.

The town began to develop extensively in the 19th century. In 1818 it became the seat of the Landkreis Johannisburg in East Prussia. The town’s population in 1876 was approximately 3,000. A railway built connecting Allenstein (Olsztyn) and Lyck (Ełk) ran through Pisz. Its water supply system and gas works were built in 1907 and its municipal slaughterhouse in 1913. The town’s industrial development focused on wood processing and metallurgy. According to the German census from 1900 its population consisted of 70,2% Mazurs.

During World War II, Pisz was 70% destroyed by fighting and occupation by the Soviet Red Army. At war’s end in 1945, it was transferred from German to Polish control and officially renamed from Johannisburg to Pisz in 1946. The name Pisz comes from the Prussian word pisa (“swamp”), owing to the muddy water from nearby Lake Roś.

Little of pre-war Pisz survived the warfare aside from its Gothic town hall, but much of Pisz has been restored in recent decades. The town is a popular place to begin sailing on the Masurian lakes. Historical sites include the ruins of the Teutonic Knights’ Johannisburg castle and the Church of St. John.