Unitary Democratic Coalition

The Unitary Democratic Coalition (Portuguese: CDU – Coligação Democrática Unitária, CDU) is an electoral and political coalition between the Portuguese Communist Party (Portuguese: Partido Comunista Português or PCP) and the Ecologist Party "The Greens" (Portuguese: Partido Ecologista "Os Verdes" or PEV). The coalition also integrates the political movement Democratic Intervention (Portuguese: Intervenção Democrática or ID).

The coalition was formed for the first time in 1987 in order to run to the simultaneous legislative election and European Parliament election that were held on July 19 of that year.

Since the beginning of the coalition, the member parties have never participated separately in any election. The Communist Party is the major force inside it and has the majority of places in the electoral lists, however, the Greens also have an important presence, for instance, electing 2 members of parliament among the 17 elected by the coalition in the 2015 legislative election. Each party has its own parliamentary group and counts as a separate party in official issues. In the 2022 Portuguese legislative election, the Greens failed to elect any representatives.

At a local level, the coalition usually presents lists in almost every municipality and both Communists and Greens may occupy first place on the lists. As the Greens have a smaller structure, the offices of the Communist Party are used as offices of the coalition.

The coalition supported the minority Socialist Costa Government (2015–2019) with a confidence and supply agreement.