Objective. Lobbying by nonprofits is a relatively new topic that has drawn attention from political science scholars and nonprofit managers. Several studies have demonstrated there to be lobbying inequalities among nonprofits, but few have compared lobbying expenditures across groups and none have taken into account how well groups have mobilized. Methods. Examining 227 groups that issue legislative "scorecards" over six terms of Congress (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010), the author uses a mix of analysis of variance and regression analysis to determine whether groups with different missions lobby at different levels and whether mobilization factors, such as revenue and membership, can help explain these differences. Results. The author finds that organizational revenue and membership predict how much most groups spend on lobbying. However, this finding does not apply to all groups. Public interest nonprofits lobby at higher levels as both their revenues and memberships increase. But business associations lobby at significantly high levels regardless of how well they mobilize. Conclusions. These results suggest that business associations view lobbying as a more necessary activity for completion of their missions than other tax-exempt organizations. (c) subsection organizations. Available at http://nccsdataweb.urban.org/PubApps/showOrgsByCategory. php?group=subsection&code= . Accessed July 15, 2012.2 This article is about lobbying, but it is worth nothing that there has been much recent discussion about nonprofits involved with elections. Most of this due to the Citizens United v. FEC (2010) ruling and the recent IRS controversy regarding 501(c)(4) applications.