Despite increasing evidence for the effectiveness of intensive short-term dynamic psychotherapy (ISTDP), evidence supporting the purported mechanisms of change in ISTDP is lacking. This systematized review aimed to describe the major theorized mechanisms of change in ISTDP, critically evaluate the emerging literature pertaining to its purported mechanisms, and explore directions for future research.A systematized search of the literature was conducted by using online databases (PsychInfo, PubMed, EMBASE, and CINAHL).Fourteen studies met inclusion criteria. The included studies explored at least one theorized ISTDP mechanism of change and attempted to operationalize or otherwise empirically examine the mechanism in relation to the therapeutic process. Examined mechanisms included "unlocking the unconscious" and specific therapist interventions.The current body of literature has several limitations, most notably the lack of a consensus definition for unlocking the unconscious. This difficulty in measuring mechanisms of change is common across therapeutic modalities and limits the validity and comparability of findings. Despite these limitations, the literature suggests a possible association between theorized mechanisms of change and positive therapy outcomes. Future research directions are discussed.