Emerging evidence suggests that physical activity and sedentary behavior [reflected in physical inactivity (PI)], might be two different phenotypes that may have distinct underlying physiological mechanisms. The purpose of this review is to summarize the existing literature on the genetic determinants of PA and PI phenotypes in humans, considering them as distinct behaviors. Completed in January 2011, this review includes family studies, twin studies, association studies, genome-wide linkage studies and genome-wide association scan (GWAs) reporting different physical activity/inactivity-related phenotypes. In regards to PA, familial aggregation studies resulted in heritability estimates ranging from 0 to 60 %, and twin studies yielded heritability estimates (a(2)) and shared environment (c(2)) scores for PA phenotypes ranging from 0.00 to 0.85 and 0.00 to 0.84, respectively. Unique environmental (e(2)) results are well dispersed from 0.12 to 0.72. Suggestive linkages were found with markers nearby different activity-related genes: EDNRB, MC4R, UCP1, FABP2, CASR, SLC9A9. Significant associations with PA phenotypes were found for Ace, Gln223ARrg, MC4R and DRD2 genes. We found one GWAs that reported novel SNPs in the PAPSS2 gene on chromosome 10q23.2 and in two intergenic regions on chromosomes 2q33.1 and 18p11.32. Heritability estimates for PI ranged from 25 to 60 % and linkage studies recorded higher LOD scores for PI versus PA. The ACE genotype was strongly associated with PI. There are potentially different genetic influences on PA versus PI phenotypes. Future studies should focus on the different genetic influences on PA and PI to improve our understanding of underlying determinants of these behaviors.