The Communist Party of Germany (Opposition) ( or , generally abbreviated as KPO or KPDO) was a communist opposition organisation established at the end of 1928 and maintaining its existence until 1939 or 1940. After the rise of Adolf Hitler and the Nazi Party to power in January 1933, the KPO existed only as an illegal and underground organization. The group initially sought to modify, later to replace, the mainstream Communist Party of Germany (KPD) headed by Ernst Thälmann. The KPO was the first national section affiliated to the International Communist Opposition (ICO).

The Lovestoneites, led by former General Secretary of the Communist Party USA (CPUSA) Jay Lovestone, were a small American oppositionist Communist movement of the 1930s. The organization emerged from a factional fight in the CPUSA in 1929 and unsuccessfully sought to reintegrate with that organization for several years.