Which types of nonprofit organizations make claims to the state by lobbying and what explains their involvement in the activity? Although many studies focus on organization-level characteristics, the authors argue that nonprofit lobbying is driven by two different dynamics that operate at the field level: cross-sector competition and social change mission. Analyzing data on nonprofit organizations in California from 1998 to 2003, the authors show that nonprofits in mission-driven fields are more likely to lobby than nonprofits in other fields, but cross-sector competition does not seem to influence lobbying at the field level. The authors also find that many organization-level characteristics matter and nonprofits with lobbying experience tend to make the activity a regular component of their organizational repertoire. These findings have a variety of implications for work on civic engagement and the authors conclude with a discussion of the implications.