Winterthur (Swiss Standard German pronunciation: [ˈvɪntərtuːr]; French: Winterthour [vintəʁtuʁ, vintɛʁ-]) is a city in the Canton of Zurich in northern Switzerland. With over 120,000 residents, it is the country's sixth-largest city by population, as well as its ninth-largest agglomeration with about 140,000 inhabitants. Located about 20 kilometres (12 mi) northeast of Zurich, Winterthur is a service and high-tech industrial satellite city within Zurich Metropolitan Area.

The official language of Winterthur is German, but the main spoken language is the local variant of the Alemannic Swiss German dialect, Zurich German. Winterthur is usually abbreviated as Winti in the local dialect and by its inhabitants.

Winterthur is connected to Germany by direct trains and has links to Zurich Airport.