What is data-driven campaigning? According to prevailing accounts, this idea describes the rise of increasingly sophisticated, highly targeted, and often invasive uses of data deployed to suppress votes, manipulate voter preferences, or boost a candidates' popularity. The power of data is seen to be transforming campaigning practice and raising democratic concerns. And yet, there is a significant problem with these ideas: we have at best a partial understanding of how data-driven campaigning is practiced, and limited clarity about its implications. Presenting data from interviews with over 300 professional campaigners in Australia, Canada, Germany, the UK and US, we provide unique insight into the components of data-driven campaigning by political parties. This book makes three key contributions. First, distinguishing between data, analytics, technology and personnel, they give unmatched descriptive insight into these four components of data-driven campaigning, revealing significant variation in its operationalization, depending on party and country context. Second, introducing a novel multi-level theoretical framework, they isolate systemic, regulatory, and party level variables that help explain the reasons for these differences. Third, they consider the implications of their findings for debates about democracy, data and technology in the 21st century. Cumulatively, these contributions reveal that data-driven campaigning is not inherently problematic. Giving voice to practitioner perspectives, through interviews and innovative vignettes, this book recasts the debate around data-driven campaigning, offering important lessons for scholars, campaigners, and policymakers alike.