Orta San Giulio (Piedmontese and Novarese: Òrta) is a town and comune (municipality) in the Province of Novara in the Italian region of Piedmont, located about 100 kilometres (62 mi) northeast of Turin and about 40 kilometres (25 mi) northwest of Novara. It is one of I Borghi più belli d'Italia ("The most beautiful villages of Italy").

The town itself is built on a promontory which juts out from the eastern bank of Lake Orta close to San Giulio Island, an island which also falls within the municipal boundaries. The frazione of Legro stands on the hill which rises behind the promontory, Corconio is some 2 kilometres (1.2 mi) further south, and again away from the lake, while Imola consists of a small number of dwellings between the two, but close to the lake on the road leading to Gozzano. The municipality borders on Pettenasco to the north, Miasino and Ameno to the east, Bolzano Novarese and Gozzano to the south, and San Maurizio d'Opaglio and Pella to the west across the lake.

It is well known for the nearby Sacro Monte, which is a site of pilgrimage and worship and, like the town itself and the island, is a popular destination for fairly small-scale tourism.