The Saitama Seibu Lions are a professional baseball team in Japan's Pacific League based north of Tokyo in Tokorozawa, Saitama Prefecture. Before 1979, they were based in Fukuoka, Fukuoka Prefecture in Kyushu. The team is owned by a subsidiary of Seibu Railway, which in turn is owned by the Seibu Holdings. The team experienced a recent period of financial difficulty, but the situation brightened when the team received a record ¥6 billion posting fee from the Boston Red Sox for the right to negotiate a contract with Daisuke Matsuzaka. Between 1978 and 2008, the team logo and mascot were based on the adult version of Kimba the White Lion, a classic Japanese anime and manga series by Osamu Tezuka. In 2004, former Seibu Lions player Kazuo Matsui became the first Japanese infielder to play in Major League Baseball.

Tokorozawa is a city located in Saitama Prefecture, Japan. As of 1 February 2024, the city had an estimated population of 343,298 in 168,939 households and a population density of 4761 persons per km². The total area of the city is 72.11 square kilometres (27.84 sq mi).