Background: The investigation of treatment mechanisms in randomized controlled trials has considerable clinical and theoretical relevance. Despite the empirical support for the effect of mindfulness-based cognitive therapy (MBCT) in the treatment of recurrent major depressive disorder (MDD), the specific mechanisms by which MBCT leads to therapeutic change remain unclear. Objective: By means of a systematic review we evaluate how the field is progressing in its empirical investigation of mechanisms of change in MBCT for recurrent MDD. Method: To identify relevant studies, a systematic search was conducted. Studies were coded and ranked for quality. Results: The search produced 476 articles, of which 23 were included. In line with the theoretical premise, 12 studies found that alterations in mindfulness, rumination, worry, compassion, or meta-awareness were associated with, predicted or mediated MBCT's effect on treatment outcome. In addition, preliminary studies indicated that alterations in attention, memory specificity, self-discrepancy, emotional reactivity and momentary positive and negative affect might play a role in how MBCT exerts its clinical effects. Conclusion: The results suggest that MBCT could work through some of the MBCT model's theoretically predicted mechanisms. However, there is a need for more rigorous designs that can assess greater levels of causal specificity.