The Constitutional Democratic Party of Japan (CDP) is a social liberal political party in Japan that was founded on 3 October 2017 as a split from the Democratic Party.
After liberal members of the Democratic Party who intended to run for election in 2017 as Kibo no To candidates were rejected on ideological grounds, DP deputy leader Yukio Edano founded the CDP to rally liberals and left-leaning members of the DPJ. The party became the largest opposition and pacifist party in 2017, and, in 2020, it merged with the Democratic Party for the People and the SDPJ to form a more united opposition. However, the party's electoral pact with the JCP, Reiwa Shinsengumi, and the remaining DPFP and SDP parties at the 2021 election failed to topple the LDP, and the CDP fell from 110 to 96 seats.
The party was mainly supported by liberal and progressive voters who prioritized social justice, human rights, and equality; by younger voters dissatisfied with the established political order and seeking education reform, affordable housing, and employment opportunities; by urban residents in cities like Tokyo, Osaka, and Nagoya who prioritized issues like transportation, environmental protection, and urban development; by labor unions who supported improved labor conditions and raising the minimum wage; and by pacifist and anti-nuclear movement supporters.