 This paper reviews the literature on sedentary behavior in adults age 18 to 65 years old. It identifies individual, social, environmental and policy-related determinants of sedentary behavior. The paper concludes that there are many factors that can contribute to sedentary behavior including age, physical activity levels, body mass index, socioeconomic status, marital, cohabitation status, neighborhood walkability, and weather. Additionally, it suggests that future research should focus on longitudinal study designs, exploring policy-related factors, further exploration of environmental factors, and the interplay between these factors. This article was authored by Grain O'Donohue, Camille Pashou, Keetley Mensa, and others.