Human nature is a very complex phenomenon. In physical therapy this complexity is enhanced by the need to understand the intersection between the art and science of human behavior and patient care. A paradigm is a set of basic beliefs that represent a worldview, defines the nature of the world and the individual's place in it, and helps to determine criteria used to select and define research inquiry. A paradigm guides scientific inquiry, not only in the manner in which an investigation is performed, but also in how the investigator defines truth and reality and how the investigator comes to know truth or reality. A paradigm guides the types of research questions that will be posed, the methodological approach to the inquiry, and criteria for assessing the trustworthiness of the inquiry. Research plays an important role in enabling physical therapists to fully embrace the values of the profession, including evidence-based practice and client-centered care, in making informed clinical decisions. However, to do so, the research provided must include not only the views of the researchers, but also the lived experiences of the clients as well. This paper provides the reader with a solid foundation in the positivist/post-positivist, constructivist, and critical theorist research paradigms and how they apply in physical therapy practice. Research perspectives in physical therapy are explored, as are implications for future practice in physical therapy.