Lausanne ( loh-ZAN, US also loh-ZAHN, French: [lɔzan] (listen)) is the capital and largest city of the Swiss French speaking canton of Vaud. It is a hilly city situated on the shores of Lake Geneva, about halfway between the Jura Mountains and the Alps, and facing the French town of Évian-les-Bains across the lake. Lausanne is located 62 kilometres (38.5 miles) northeast of Geneva, the nearest major city.

The municipality of Lausanne has a population of about 140,000, making it the fourth largest city in Switzerland after Basel, Geneva, and Zurich, with the entire agglomeration area having about 420,000 inhabitants (as of January 2019). The metropolitan area of Lausanne-Geneva (including Vevey-Montreux, Yverdon-les-Bains, Valais and foreign parts), commonly designated as Arc lémanique was over 1.3 million inhabitants in 2017 and is the fastest growing in Switzerland.

Initially a Celtic and Roman settlement on the shores of the lake, Lausanne became a town at the foot of Notre Dame, a cathedral built in the 12th century. In the 20th century, Lausanne became a focus of international sport, hosting the International Olympic Committee (which has recognized the city as the "Olympic Capital" since 1994), the Court of Arbitration for Sport and some 55 international sport associations. It lies in a noted wine-growing region. The city has a 28-station metro system, making it the smallest city in the world to have a rapid transit system. Lausanne hosted the 2020 Winter Youth Olympics.