Karuizawa Station is served by the JR East Hokuriku Shinkansen high-speed line from Tokyo to Kanazawa via Nagano.

It is also a terminal station for the 65.1 kilometer Shinano Railway Line which operates between Karuizawa and Nagano.

The station began service on December 1, 1888, as the terminal of the Japanese Government Railways between Naoetsu (near the Sea of Japan coast) and Karuizawa.

On October 1, 1997, JR East opened the Nagano Shinkansen with a stop at Karuizawa.

At the same time, JR East ceased to operate the conventional Shinetsu Main Line between Yokokawa and Shinonoi, of which, the section between Yokokawa and Karuizawa (Usui Pass) was closed permanently and the remaining section was transferred to Shinano Railway.