Case conceptualization is an essential clinical activity in which clinicians, in one form or another, gather and synthesize data about their clients in order to formulate clinical pictures and maximize therapeutic gains. However, a myriad of methods of case conceptualization that vary in complexity and theoretical bases currently reflects an almost complete lack of standardization in this most fundamental activity of mental health treatment. The lack of standardization in case conceptualization is especially daunting to trainees and clinicians who are early in their careers. This special section, comprising 5 articles, introduces thematic mapping, a transtheoretical and transdiagnostic method of case conceptualization. The method aims to overcome or minimize many of the problems inherent in current practice. In this first article, we provide a rationale for the special section and lay the groundwork for the subsequent four articles. Overall, we assert that thematic mapping holds promise as a systematic method of case conceptualization.