The Liberal Democratic Party , frequently abbreviated to LDP or Jimintō (自民党), is a major conservative and Japanese nationalist political party in Japan.

The 1955 system (55年体制), also known as the one-and-a-half party system, is a term used by scholars to describe the dominant-party system that has existed in Japan since 1955, in which the Liberal Democratic Party (LDP) has successfully held by itself or in coalition with Komeito a majority government nearly uninterrupted, with opposition parties largely incapable of forming significant or long lasting alternatives, other than for brief stints in 1993–1994 and 2009–2012. The terms 1955 system and the one-and-a-half party system are credited to Junnosuke Masumi, who described the 1955 system as "a grand political dam into which the history of Japanese politics surge".