Much has been written about the historic nature of the Obama campaign. The multi-year, multi-billion dollar operation elected the nation's first black president, raised and spent more money than any other election effort in history, and built the most sophisticated voter targeting technology ever before used on a national campaign. But what is missing from these accounts is an understanding of how Obama for America organized its formidable army of 2.2 million volunteers - over eight times the number of people who volunteered for democratic candidates in 2004. Unlike previous field campaigns that drew their power from staff, consultants, and paid canvassers, the Obama campaign's capacity came from unpaid local citizens who took responsibility for organizing their own neighborhoods months-and even years-in advance of election day. In so doing, Groundbreakers argues, the campaign enlisted citizens in the often unglamorous but necessary work of practicing democracy. How did they organize so many volunteers to produce so much valuable work for the campaign? This book describes how. Hahrie Han and Elizabeth McKenna argue that the legacy of Obama for America extends far beyond big data and micro targeting - to a transformation of the traditional models of field campaigning. As the first book to analyze a presidential contest from the perspective of grassroots volunteers, Groundbreakers makes the case that the Obama ground game was revolutionary in two regards not captured in previous accounts. First, the campaign piloted and scaled an alternative model of field campaigning that built the power of a community at the same time that it organized it. Second, the Obama campaign changed the individuals who were a part of it, turning them into leaders. Obama the candidate might have inspired volunteers to join the campaign, but it was the fulfilling relationships volunteers had with other people and their deep belief that their work mattered that kept them active. Moreover, the lessons learned from the Obama campaign have and will continue to transform the nature of future campaigns, in both political and civic movements, nationally and internationally. Groundbreakers proves that presidential campaigns are still about more than clicks, big data and money, and that one of the most important ways that a campaign develops its capacity is by investing in its human resources.