Baldassarre Longhena (Venice, 1598 – Venice, 1682), was a 17th century Venetian architect, who worked mainly in Venice itself, where he was one of the greatest exponents of Baroque architecture of the period.

He studied under the architect Vincenzo Scamozzi and after Scamozzi's death completed his monumental Procuratie Nuove in St. Mark's Square, a complex of imposing residences and offices for officials of the Venetian Republic that gives the square its appearance today.

His best-known work is the Basilica di Santa Maria della Salute begun in 1631 to give thanks for the cessation of a plague in Venice. This two domed church on the peninsular between the Grand Canal and the Zattere is one of the city's best-known landmarks. The main entrance, modeled on the Roman triumphal arch, was later copied in successive churches and cathedrals, in Venice and elsewhere.

He designed many other churches in the city among them the Chiesa dell'Ospedaletto and Santa Maria degli Scalzi built between 1656 and 1680 although the façade of this church was designed by Giuseppe Sardi.

One of his largest designs was the cathedral at Chioggia, executed between 1624 and 1647. On the completion of the cathedral he was asked to design the palazzo, later to be called Ca' Rezzonico, on the Grand Canal in Venice, although he died before its completion. It was finally finished according to his designs over 100 years later.