BACKGROUND: So-called 'third wave' cognitive and behavioural therapies represents a new generation of psychological therapies that are increasingly being used in the treatment of psychological problems. However, the effectiveness and acceptability of third wave cognitive and behavioural therapy (CBT) approaches as a treatment for depression compared with other psychological therapies remain unclear. OBJECTIVES: 1. To examine the effects of all third wave CBT approaches compared with all other psychological therapy approaches for acute depression.2. To examine the effects of different third wave CBT approaches (ACT, compassionate mind training, functional analytic psychotherapy, extended behavioural activation and metacognitive therapy) compared with all other psychological therapy approaches for acute depression.3. To examine the effects of all third wave CBT approaches compared with different psychological therapy approaches (psychodynamic, behavioural, humanistic, integrative, cognitive-behavioural) for acute depression. SEARCH METHODS: We searched the Cochrane Depression, Anxiety and Neurosis Group Specialised Register (CCDANCTR to 01/01/12), which includes relevant randomised controlled trials from The Cochrane Library (all years), EMBASE (1974-), MEDLINE (1950-) and PsycINFO (1967-). We also searched CINAHL (May 2010) and PSYNDEX (June 2010) and reference lists of the included studies and relevant reviews for additional published and unpublished studies. An updated search of CCDANCTR restricted to search terms relevant to third wave CBT was conducted in March 2013 (CCDANCTR to 01/02/13). SELECTION CRITERIA: Randomised controlled trials that compared various third wave CBT with other psychological therapies for acute depression in adults. DATA COLLECTION AND ANALYSIS: Two review authors independently identified studies, assessed trial quality and extracted data. Study authors were contacted for additional information where required. We rated the quality of evidence using GRADE methods. MAIN RESULTS: A total of three studies involving 144 eligible participants were included in the review. Two of the studies (56 participants) compared an early version of acceptance and commitment therapy (ACT) with CBT, and one study (88 eligible participants) compared extended behavioural activation with CBT. No other studies of third wave CBT were identified. The two ACT studies were assessed as being at high risk of performance bias and researcher allegiance. Post-treatment results, which were based on dropout rates, showed no evidence of any difference between third wave CBT and other psychological therapies for the primary outcomes of efficacy (risk ratio (RR) of clinical response 1.14, 95% confidence interval (CI) 0.79 to 1.64; very low quality) and acceptability. Results at two-month follow-up showed no evidence of any difference between third wave CBT and other psychological therapies for clinical response (2 studies, 56 participants, RR 0.22, 95% CI 0.04 to 1.15). Moderate statistical heterogeneity was indicated in the acceptability analyses (I(2) = 41%). AUTHORS' CONCLUSIONS: Very low quality evidence suggests that third wave CBT and CBT approaches are equally effective and acceptable in the treatment of acute depression. Evidence is limited in quantity, quality and breadth of available studies, precluding us from drawing any conclusions as to their short- or longer-term equivalence. The increasing popularity of third wave CBT approaches in clinical practice underscores the importance of completing further studies to compare various third wave CBT approaches with other psychological therapy approaches to inform clinicians and policymakers on the most effective forms of psychological therapy in treating depression.