Cognitive Behavioral Therapy (CBT) refers to a treatment approach with strong empirical support for its efficacy for various disorders and populations. The goal of the present review was to provide a comprehensive survey of meta-analyses examining the processes of CBT, namely: treatment processes (cognitive reappraisal, behavioral strategies, emotional regulation, motivation strategies, and psychoeducation) and in-session processes (alliance, goal consensus and collaboration, feedback, group cohesion, and homework). We identified 558 meta-analyses of CBT, and 30 meta-analyses met our inclusion criteria as reviews of process-outcome relations. For treatment processes, the strongest support currently exists for cognitive (n = 8 meta-analyses) and behavioral strategies (n = 3 meta-analyses) as change processes in CBT for anxiety disorders and depression. For in-session processes, the strongest support currently exists for the role of the alliance (n = 8 meta-analyses) and homework assignments (n = 6 meta-analyses) as predictors of outcome. Overall, the evidence base for process-outcome relations in CBT is just emerging. Additional research is needed to examine the range of treatment processes in various clinical contexts. Moreover, except for a meta-analysis on collaboration, no meta-analytic studies have been reported on CBT-specific elements of the therapeutic relationship, such as collaborative empiricism and Socratic dialogue.