Although it is true that in the field of psychotherapy research, increasingly innovative qualitative designs appeared worldwide, which in some way guided the work carried out in Chile, we also created and proposed our methods, designs, and techniques for the analysis of subjective data that have allowed us to deepen our knowledge of the psychotherapeutic process. In this sense, we seek to highlight the importance of the systematic observation strategy as one of the most fundamental when investigating different phenomena in the social sciences, and in which the role of the researcher as main instrument is clearer than ever. This chapter intends to show how qualitative methodology has allowed us to generate results through innovative, complex, and pioneering designs, without seeking to justify the different methods used to generate new knowledge in the psychotherapeutic field. The aim is to highlight some epistemological, philosophical, axiological, and methodological assumptions when formulating, executing, interpreting, and evaluating the different investigations carried out basically with a constructivist paradigm with certain post-positivist touches. It also aims to allude to some main ethical dilemmas that arise when producing data generated in a constructivist paradigm. It also aims to allude to some main ethical dilemmas that arise when producing data generated in the most naturalistic settings possible and which are qualitatively interpreted in depth based on an intersubjective consensus that respects, encourages, and agrees on the different perspectives on the same phenomenon. Some results will be discussed that allowed us to generate products that are being used today to formulate new research proposals and that are also being used to guide the clinical work of psychotherapists and the learning processes during the training of psychology students in the clinical area, from the use of models and manuals generated from research but also from the acquisition of new therapeutic skills based on systematic observation.