The Asama-Sansō incident was a hostage crisis and police siege at a mountain lodge near Karuizawa in Nagano Prefecture, Japan, which lasted from February 19 to February 28, 1972. The police rescue operation on the final day of the standoff was the first marathon live television broadcast in Japan, lasting 10 hours and 40 minutes.

Karuizawa is a resort town located in Nagano Prefecture, Japan. As of 1 October 2016, the town had an estimated population of 20,323 in 9897 households, and a population density of 130 persons per km2. The total area of the town is 156.03 km2 (60.24 sq mi). Karuizawa, one of the oldest and most famous summer resorts in Japan, has been visited by many people from around the world since the 19th century.