Research on individual, situational, and neighborhood/community factors ignore the reciprocal and interactive relationships among these variables at different levels of effect. Known risk factors for youth violence include population indicators such as male gender and ages 15-25, biological factors such as high testosterone levels and high levels of lead, psychological characteristics such as impulsivity and concentration problems. Other individual factors include family factors such as marital conflict and child abuse or neglect, school factors such as high rates of truancy and low bonding to school, and peer factors such as delinquent or violent peers or siblings and gang membership. Situational factors include drug abuse and the presence of a weapon. Neighborhood factors include poverty and population density, high residential mobility, community disorganization, and media influences. Nevertheless, the study of violence is still at an early stage. Understanding of violence must move from the mere identification of static factors associated with violence to a more dynamic assessment of their interactions over time and in different circumstances and populations. More research and more sophisticated statistical and methodological techniques are needed to model a phenomenon as complex, multiply determined, dynamic, and protean as youth violence. Table and 106 references