Aim: In this paper we review the current literature on the clinical problem that some patients do not achieve response after adequately conducted psychotherapy. We explicate our understanding of nonresponse and treatment resistance including the operational definitions, summarize the theoretical explanations and empirical studies and put forward possible study designs and treatment options. Methods: Literature search using PubMed and Web of Science. Results: For the domain of psychotherapy, the term treatment resistance does not seem appropriate; instead, we use the more descriptive terms nonresponse and recurrent nonresponse. Generally, this topic is far less represented in psychotherapy than in pharmacotherapy. Controlled switching studies with a switch from pharmacotherapy to psychotherapy are rare and those switching from one psychotherapeutic approach to another are nearly nonexistent. Building on clinical considerations, we propose a flow-chart for clinical decision making after nonresponse in psychotherapy. Discussion: Learning from errors is highly beneficial. This principle should be more consistently followed up in psychotherapy research as well as in supervision and training. Guidelines should include consensual and evidence-based advice on how to deal with nonresponse and recurring nonresponse.