Purpose: To assess the effects of supporting labor market interventions for adults outside the labor market who are long-term social assistance recipients, and to present participant experiences of return-to-work interventions. Method: A systematic review where direct and indirect client interventions were synthesized. We included 26 quantitative studies (seven randomized and 19 based on register data about 5.8 million persons), and 14 qualitative studies. Results: Effective programs to enable long-term social assistance recipients to enter and retain employment are workplace training, extensive or long-term training, work support programs in regular activities (moderate certainty of evidence). Up until February 2022, this report updates previous knowledge about the effects of education, internships and work practice, and employer subsidies together with new knowledge about the effects of case managers' working methods for the target group. Evidence gaps are addressed. Discussion: Strengths and limitations, practice, policy and research implications, and ethical considerations are discussed.