Mental disorders are among the core health challenges of the past and upcoming centuries. In Europe, more than one third of the population (about 165 million individuals) suffers from mental disorders every year, demonstrating a great need for both effective prevention programs and treatments. However, a substantial proportion of patients still do not show a clinically meaningful response to available interventions. One reason that has been repeatedly discussed in this context is the logic of current diagnostic systems. Traditional diagnostic systems, such as the DSM-5 and the ICD-11, define mental disorders as distinct categories of co-occurring symptom clusters. These tools, however, are purely descriptive, mainly based on patients’ symptom reports and clusters, and make no assumptions about the etiological mechanisms underlying disorder onset or maintenance. Alternative approaches in clinical psychology started to follow basic psychological disciplines, inspired by cognitive, emotional, biological, social, and developmental psychology. They suggest diverse developmental models for unified symptomatology within single diagnostic categories, as well as transdiagnostic pathogenic mechanisms. In particular, the research field of experimental psychopathology and psychotherapy (EPP) has contributed important findings to this translational perspective. Among other goals, EPP research aims to study the causal relationship between psychological and behavioral processes in maladaptive experience related to the psychopathological symptoms but also their modulation using a wide range of experimental designs. EPP takes into account the necessary perspectives on heterogeneous etiological mechanisms within diagnostic categories and transdiagnostic mechanisms of action. It thus follows the traditional view of maladaptive processes from the perspective of basic psychology without necessarily referring to specific diagnostic groups. However, the majority of currently recommended evidence-based psychological treatments was not strongly based on basic research, calling for a stronger and more explicit consideration of the EPP findings.