Loneliness and social isolation are major problems for older adults. Interventions and activities aimed at reducing social isolation and loneliness are widely advocated as a solution to this growing problem. The aim of this study was to conduct an integrative review to identify the range and scope of interventions that target social isolation and loneliness among older people, to gain insight into why interventions are successful and to determine the effectiveness of those interventions. Six electronic databases were searched from 2003 until January 2016 for literature relating to interventions with a primary or secondary outcome of reducing or preventing social isolation and/or loneliness among older people. Data evaluation followed Evidence for Policy and Practice Information and Co‐ordinating Centre guidelines and data analysis was conducted using a descriptive thematic method for synthesising data. The review identified 38 studies. A range of interventions were described which relied on differing mechanisms for reducing social isolation and loneliness. The majority of interventions reported some success in reducing social isolation and loneliness, but the quality of evidence was generally weak. Factors which were associated with the most effective interventions included adaptability, a community development approach, and productive engagement. A wide range of interventions have been developed to tackle social isolation and loneliness among older people. However, the quality of the evidence base is weak and further research is required to provide more robust data on the effectiveness of interventions. Furthermore, there is an urgent need to further develop theoretical understandings of how successful interventions mediate social isolation and loneliness.