Poor people's movements describes contentious collective actors that are considered to be particularly powerless or weak in resources compared to other members of a community. Often, the term is used to describe spontaneous mass protest by members of social groups that are at the lower end of a socioeconomic scale or in a particularly marginalized position in a society, such as the homeless or the unemployed. Research into poor people's movements has shown, however, that these movements share similar organizational and coordinated social action to other movement activity. This entry examines the shared characteristics of these movements, how studies of poor people's movements over the past decades have changed, and the insights we have gained from studies on social movement activity of the poor for social movement theory.