Community colleges provide postsecondary education to millions of students in the United States each year, but their graduation rates are low. Many community colleges have implemented interventions to help students persist in college and earn degrees. MDRC has studied many such interventions; several of them improved students' academic outcomes, but the effects varied. This report synthesizes results from MDRC's studies. The data include findings from 30 studies of 39 interventions at 45 colleges. The interventions included different components designed to help students succeed: enhanced advising; enhanced tutoring; financial support; instructional reform; learning communities (which enroll small groups of students together in two or more courses); promoting full-time enrollment in fall and spring, summer enrollment, or both; and success courses (designed to help new students navigate college and build relevant skills). MDRC conducted a quantitative synthesis of the studies' results to examine the relationship between various intervention features and effects on selected student outcomes. This report draws from the quantitative synthesis and also from detailed information on how the interventions were implemented. The research also points to some areas for further exploration. Those areas include how to support part-time community college students effectively, the implementation and effects of programs targeting students in rural areas and in small colleges, and the potential role of community college interventions in reducing racial inequality in students' academic outcomes.