Associations between inadequate and excessive gestational weight gain (GWG) and adverse perinatal outcomes are well documented. Less is known about potential determinants of GWG. Much of the existing research has focused on pre-pregnancy BMI, diet, and physical activity, leaving other social and behavioral determinants relatively unexplored. The objective of this study is to review empirical studies that treat GWG as an outcome and summarize the biological, behavioral, social, and environmental risk factors associated with GWG. Strengths, weaknesses, and gaps in the literature will be discussed.