Allan J. Cigler & Burdett A. Loomis 
Interest Group Politics [PDF ebook] 

With its broad spectrum of scholarship on interest groups past and present, Interest Group Politics brings together noted political scientists to provide comprehensive coverage and cutting-edge research on the role and impact of interest groups in U.S. politics, all geared to an undergraduate audience. In the wake of the Citizens United decision and the growth of lobbying into a multi-billion dollar industry, this trusted classic provides students with a guide to the influence and reach of interest groups.