Sassari (in Italian and Sassarese, a Corsican dialect; either Sassari or Tathari in southern Sardinian), is a town in the province of Sassari in Sardinia, Italy. The second-largest town on the island in terms of population (est. 120,000), Sassari is one of the most ancient Sardinian towns, and contains perhaps the best collection of Sardinian art.

Its university has a high reputation, especially in jurisprudence studies, and in its libraries are a number of ancient documents, among them the famous Carta de Logu (the constitution issued by Giudichessa Eleonora d'Arborea), or the Condaghes, Sardinia's first legal codes and the first documents written in the Sardinian language (11th century). The dialect spoken at Sassari is not Sardinian however, but Corsican language variety as in most of the Northern part of Sardinia.

Sassari is also the birthplace of many famous Sardinians, among them the former president of the Italian Republic, Francesco Cossiga, his cousin Enrico Berlinguer, national secretary in the 1970s and leader of the most important Communist party in Western Europe, and their uncle Antonio Segni, another former president of the Italian Republic.

During Catalan domination the city was known as Sàsser.