The under-representation of women in physical science, technology, engineering, and mathematics (PSTEM) career fields is a persistent problem. This paper summarizes an extensive review of the literature pertaining to the many issues that surround this problem. The review revealed a wide range of viewpoints and a broad spectrum of research methodologies used to analyze the multiple factors associated with the under-representation of women in PSTEM career fields. It used four frameworks to examine the issue: social psychological framework: internal conflict models; environmental and economic framework: external conflict models; comprehensive framework: integrated models; and critical feminist framework: alternate assumptions models. Overall, regarding internal conflicts, confidence issues were found to be a barrier, and goal-orientation an asset. Regarding external conflicts, negative environments were offset by positive social support networks. Regarding integrated models, good preparation and good advising were necessary, but not sufficient, to sustain commitment. Regarding the feminist perspective, women avoid intervention strategies that label them as defective or try to fit them to the mold or a male-dominated paradigm. (Contains 83 references.) (SM)