The findings indicate that weapon carrying was strongly influenced by peers among this sample. In examining weapons carrying status effects among peers, the study found that weapon carrying was related to an increase in the number of friendship nominations received by peers and reduced the number of given nominations. In addition, peer-reported aggressiveness predicted weapons carrying 1 year later. These findings suggest that weapon carrying by adolescents stems from a complex interaction between the attraction of weapon carriers for peer affiliation, peer influence in friendship networks, and the appeal to peers of individual aggression symbolized by weapon carrying. To the authors knowledge, this is the first study in which the effects of peer influence were unraveled from selection effects on weapon carrying, using sophisticated statistical modeling and in which the roles of personal aggression and vulnerability were also considered. Participants were asked to indicate the number of times they carried a gun, knife, or other weapon (e.g., box cutters or brass knuckles), each in the previous 60 days. This encompassed both in-school and out-of-school occasions. Participants were provided with a list of all same-gender peers in their grade and asked to nominate their best friends. A peer-nomination inventory was used to assess both aggression and vulnerability. For the statistical analyses, the SIENA program was used to estimate an actor-based model for the co-evolution of networks and behaviors across time, as well as to perform the statistical estimation of a stochastic actor-based model of network dynamics (Snijders, 2001, 2005). 4 tables and 91 references