Behavioral activation (BA) treatments for depression require patients to increase overt behavior to bring them in contact with reinforcing environmental contingencies. This meta-analysis sought to identify all randomized controlled studies of BA, determine the effect of this approach, and examine the differential effectiveness of variants. Thirty-four studies with 2,055 participants reporting symptoms of depression were included. The pooled effect size indicating the difference between BA and control conditions at posttest was 0.78. For participants who satisfied the criteria for major depressive disorder, the overall effect size of 0.74 remained large and significant. No differences in effectiveness between BA and cognitive therapy were found. BA may be considered a well-established and advantageous alternative to other treatments of depression.