Young people in disadvantaged neighborhoods are more likely to be involved in serious lawbreaking activity than are their peers from other areas. This situation has negative consequences for both the youth and their communities, including in the realms of education, employment, exposure to abuse, psychological development, public safety, and local norms. Understanding the situated agency of members of this population—their engagement in purposive action as related to their contexts—can help promote effective contextual interventions. This study developed a conception of marginal life space as an expansion of the idea of neighborhood disadvantage and used ethnographic methods to explore the life spaces and situated agency of young people who have been involved in serious lawbreaking. In-depth interviews, neighborhood mapping, and neighborhood walks and observations were conducted with fourteen adolescents and young adults who live in areas marked by structural marginality. Interview transcripts and field notes were inductively coded, and codes were grouped into patterns in order to elicit themes. Four central findings emerged in this exploratory study. One, study participants have multiple meaningful spaces in their lives. While all have life spaces marked by structural marginality, these life spaces, which form the context of their situated agency, are fundamentally individual. Two, four situations that catalyze involvement in serious lawbreaking were identified: peer pressure and the desire to fit in, the need or desire for money, family-related stress, and interpersonal conflicts. Three, the streets constitute an experiential space that is both supra-geographic and sub-geographic; that is characterized by violence and alternative institutions; and that is often a part of participants’ life spaces. Four, participants enacted agency relative to the streets by engaging in serious lawbreaking there, by crossing in and out of the streets, and by staying out of the streets. These findings advance understandings about how young people in marginalized communities, particularly those with histories of serious lawbreaking, experience space and enact situated agency. In so doing, the findings give voice to the young people and can inform contextual interventions that will create more enriching communities.