Background: Physical activity(PA) during pregnancy provides physical and psychological benefits for mother and child. U.S. guidelines recommend ≥30 min of moderate exercise for healthy pregnant women most days of the week; however, most women do not meet these recommendations. Theory assists in identifying salient determinants of health behavior to guide health promotion interventions; however, the application of theory to examine PA among pregnant women has not been examined cohesively among multiple levels of influence(e.g.,intrapersonal, interpersonal, neighborhood/environmental, and organizational/political). Subsequently, this systematic review aims to identify and evaluate the use of health behavior theory in studies that examine PA during pregnancy.Methods: Articles published before July 2014 were obtained from Pub Med and Web of Science. Inclusion criteria applied were:(1) empiricallybased;(2) peer-reviewed;(3) measured factors related to PA;(4) comprised a pregnant sample; and(5) applied theory. Fourteen studies were included. Each study’s application of theory and theoretical constructs were evaluated.Results: Various theories were utilized to explain and predict PA during pregnancy; yet, the majority of these studies only focused on intrapersonal level determinants. Five theoretical frameworks were applied across the studies—all but one at the intrapersonal level. Few determinants identified were from the interpersonal, neighborhood/environmental, or organizational/political levels.Conclusion: This systematic review synthesized the literature on theoretical constructs related to PA during pregnancy. Interpersonal, community,and societal levels remain understudied. Future research should employ theory-driven multi-level determinants of PA to reflect the interacting factors influencing PA during this critical period in the life course. Theory of Physical Activity (PA) during pregnancy provides physical and psychological benefits for mother and child. US guidelines recommend ≥30 min of moderate exercise for healthy pregnant women most days of the week; however, most women do not meet these recommendations. Theory assists in identifying salient determinants of health behavior to guide health promotion interventions; however, the application of theory to examine PA among pregnant women has not been examined cohesively among multiple levels of influence (eg, intrapersonal, interpersonal, neighborhood / environmental, and organizational / political This systematic review aims to identify and evaluate the use of health behavior theory in studies that examine PA during pregnancy. Methods: Articles published before July 2014 were obtained from Pub Med and Web of Science. Inclusion criteria applied were: (1 ) empirically based; (2) peer-reviewed; (3) measured factors related to PA; (4) comprised a pregnant sample; a Each study’s application of theory and theoretical constructs were both as. Results: Various theories were utilized to explain and predict PA during pregnancy; yet, the majority of these studies only focused on intrapersonal level determinants Five theoretical frameworks were applied across the studies-all but one at the intrapersonal level. Few determinants were from the interpersonal, neighborhood / environmental, or organizational / political levels. Confluence: This systematic review synthesized the literature on theoretical constructs related to PA interpersonal, community, and societal levels remain understudied. Future research should employ theory-driven multi-level determinants of PA to reflect the interacting factors influencing PA during this critical period in the life course.