Ōtsu is the capital city of Shiga Prefecture, Japan. As of 1 October 2021, the city had an estimated population of 343,991 in 153,458 households and a population density of 740 persons per km2. The total area of the city is 464.51 square kilometres (179.35 sq mi).

The Ōtsu incident was an unsuccessful assassination attempt on Nicholas Alexandrovich, Tsarevich of Russia on 11 May [O.S. 29 April] 1891, during his visit to Japan as part of his eastern journey.