Behavior Therapy-as well as its three generations-has been shown to be the psychotherapeutic technology with the most empirical evidence in clinical and health psychology. However, each of its generations is based on different philosophical foundations. In this paper, we briefly present their historical background, their strengths, and the possible drawbacks that we find in each one. First, behaviorism (methodological and radical) and its various techniques based on the principles of learning, followed by the emergence of cognitive-behavioral therapies in a historical context marked by cognitivism and, today, the most effective technique for a wide variety of cases. Finally, those known as third generation (or contextual) therapies, a technology derived from functional contextualism that is the basis of these therapies. As conclusions, the relevance of the debate surrounding the object of study of psychology and the adherence to evidence-based psychological treatments is highlighted.