Theoretical research in HRD has established itself and is now at a point where many avenues exist for further contributions to the field. But what kinds of theoretical research appear to be needed at this stage in the development of HRD? This paper identifies areas in which further research in theory and theory building might be conducted. Possible areas for future research include new HRD theory, theory-building research methods, HRD's theoretical foundation, and published work that includes both the theory-building research process and the theory itself. The paper argues that as more theory is being developed, the justification of the need for theory becomes more important. Considering the merits of alternative theoretical contributions, HRD professionals are asked to make judicious choices about the direction of future theoretical research. The implications of this study for further research and professional practice are provided.