Boys may follow various developmental pathways that lead to increasingly disruptive and delinquent behavior. To most parents, teachers, youth workers, mental health professionals, and juvenile justice practitioners, the development of disruptive and delinquent behavior in boys may appear erratic and unpredictable. This bulletin summarizes longitudinal research from the Pittsburgh Youth Study, a principal component of the Office of Juvenile Justice and Delinquency Prevention's Program of Research on the Causes and Correlates of Delinquency, which documented three developmental pathways that boys follow as they progress to more serious problem behaviors. Each pathway represents conceptually similar behaviors that unfold over time, which include: conflict with authority (defiance and running away), covert actions (lying and stealing), and overt actions (aggression and violent behavior). An important finding from these analyses is the latency period that occurred between physical fighting or violent episodes. Future analyses will focus on factors in boys' lives that increase the risk of pathway onset, penetration, and persistence. Attention will also be paid to the influence of community factors and peer influences. Multiple graphs, charts, and illustrations are included. (MKA)