Human functioning and rehabilitation research can be organized into 5 distinct scientific fields. The objective of this paper is to provide conceptual descriptions and to outline selected research domains for 4 of the 5 distinct scientific fields. A conceptual description of the biosciences in rehabilitation and the presentation of respective research domains are beyond the scope of this paper. The research domains of the human functioning sciences can be identified and described according to the generic research process, which involves theory building and observation. The according domains include theory and models of human functioning, classification and measurement of functioning, functioning epidemiology and functioning impact assessment. The research domains of the integrative rehabilitation sciences can be identified and described by drawing on the public health approach. They include rehabilitation services research, rehabilitation intervention research and rehabilitation administration and management. There are many conceivable research domains within the realms of the biomedical rehabilitation sciences and engineering. They are often defined in relation to an organ system or in relation to an intervention approach. The research domains of the professional rehabilitation sciences are well established and include professional standards and guidelines for the provision of best care, rehabilitation quality management, scientific education and training of professionals in rehabilitation, and development and evaluation of the rehabilitation team.