This study reviews systems theory and thinking (ST&T) as a foundational discipline or theory in human resource development (HRD) research and practice. Using systematic evidence review (SER) of the literature and mapping analysis of HRD curricula across some leading U.S. universities, disconnect between theory and practice of ST&T is discussed. The use of SER of the literature in HRD research is an important aspect of this study. The study recommended the incorporation of more ST&T courses into the HRD undergraduate and graduate curricula. Recommendations of how systems thinking can become more relevant to HRD research and practice are offered.