Supported playgroups are community-based services that provide low intensity family support, through regular group sessions for parents and their young children. Led by a playgroup facilitator, the program aims to enrich children's early learning, enhance positive parenting behaviors, provide social connections for parents, and enable access to other community services. Despite high community acceptance and government investment, little is known about the extent to which such services are effective. This paper reports findings from a systematic review of research on supported playgroups and their effectiveness to improve child, parent, and community outcomes. Thirty-four studies were included, of which 28 were conducted in Australia. Programs targeted a diverse range of families who were considered socially disadvantaged. Seven studies employed experimental or quasi-experimental designs from which reliable evidence for effectiveness could be established. A high proportion of studies were qualitative and included action research, case studies, or ethnographies. A range of qualitative and quantitative measures were used to assess child, parent, and community outcomes. While findings suggested that supported playgroup programs were highly valued by parents and other stakeholders, rigorous evidence of effectiveness for achieving desired improvements in child outcomes or parenting behavior was rare and limited by low quality study designs. More explicit theories of change about how different types of supported playgroup programs can meet diverse family needs are required. Such theories of change would provide directions for specific content and delivery approaches that could address and improve different child and parent outcomes targeted to specific populations of attending families.