This work posits and answers the question about 'What is an evidence-based case formulation?' It tries to shed some light on the topic by proposing three key criteria that any therapist could follow to assess a particular model of case formulation (CF), or when taking into consideration his or her own practice: The first criterion relates to the grounding of the CF's core hypothesis on a theory supported by a solid and relevant evidence; the second criterion relates to the features of the kind of reasoning, in which the clinical judgement that nurtures the formulation is based; and the third criterion, that relates to the extent in which a given formulation is founded on a structured model of CF. Furthermore, the background of evidence-based CF as a form of Evidence-Based Practice in Psychology (EBPP) is reviewed, as well as what constitutes appropriate evidence in CF. An evidence-based, systematic framework for CF is also provided and explained.