The epistemologic frame of nursing pretends to show, panoramically, the evolution of nursing knowledge. The first aspect is a clarification of the meaning of a professional discipline and its components: perspective, domain, definitions, concepts and models of knowledge. From the definition of nurse’s discipline as “care study of the experience of human health”, its inmersion in alternated paradigms of science and the definition of discipline’s visions (paradigms). Likewise, the elements of discipline and practice are compared, according to the structural hierarchy of knowledge. To explain the nursing knowledge terms,the carper’s models of knowledge are analyzed: empirical, ethical personal and esthetical. The second part of article explains the necessity to relate theory, practice and research, as fundamental basis for the development of practice, and nursing theories are also discussed, to analyze finally the utility of medium range theory for practice and research. At the end, a figure taken from Liehr and Smith, wich contains medium range theories of nursing and its posibilities for practical application, helps to clarify concepts.