This review addresses peer group influences on adolescent smoking with a particular focus on recently published longitudinal studies that have investigated the topic. Specifically, we examine the theoretical explanations for how social influence works with respect to adolescent smoking; discuss the association between peer and adolescent smoking; consider socialization and selection processes with respect to smoking; investigate the relative influence of best friends, close friends, and crowd affiliations; and examine parenting behaviors that could buffer the effects of peer influence. Our review indicates the following with respect to adolescent smoking: (a) substantial peer group homogeneity of smoking behavior; (b) support for both socialization and selection effects, although evidence is somewhat stronger for selection; (c) an interactive influence of best friends, peer groups, and crowd affiliation; and (d) an indirect protective effect of positive parenting practices against the uptake of adolescent smoking. We conclude with implications for research and prevention programs.