Abstract Biomechatronic systems integrate mechanisms, sensor integration, control strategies, human-robot interaction, and signal processing techniques. This chapter stresses the biomechatronic conception of robotic agents that interact with patients undergoing rehabilitation programs. In this context, the main role of social robotic agents is to act as companions or assistants in a specific task, which is intended improve patients’ performance or increase engagement during the therapy. Social robots are required to contain a series of features that allow them to interact in an effective way, providing adaptability and flexibility to human environments. In this work, two robot-based therapy models are presented. The first intervention with a social robot was held in a cardiac rehabilitation service. Subsequently, this work has been extended to a neurological rehabilitation scenario. That way, the corresponding clinical context in which the system was deployed is described, followed by the proposed custom human-computer interface that was designed with two purposes. In the first instance, the interface allows the patient to observe the acquired sensory data during the therapy. Likewise, this system serves as a means of communication between the robot and the user. Two experimental studies were performed in the cardiac and neurological rehabilitation contexts. Important results showed that the robot assistance during the therapy has a positive impact, which is reflected in the decreasing of risk factors such as high heart rate values or fatigue perception and the improvement of patients’ performance indicators such as cervical and thoracic postures. A positive attitude toward the robot role and patients was observed, and also greater motivation for patients to follow the rehabilitation treatment and improve their own performance according to the robot's interaction.