With the advent of digital devices and software, self-tracking practices have gained new adherents and have spread into a wide array of social domains. The Quantified Self movement has emerged to promote 'self-knowledge through numbers'. In this groundbreaking book Deborah Lupton critically analyses the social, cultural and political dimensions of contemporary self-tracking and identifies the concepts of selfhood and human embodiment and the value of the data that underpin them. The book incorporates discussion of the consolations and frustrations of self-tracking, as well as about the proliferating ways in which people's personal data are now used beyond their private rationales. Lupton outlines how the information that is generated through self-tracking is taken up and repurposed for commercial, governmental, managerial and research purposes. In the relationship between personal data practices and big data politics, the implications of self-tracking are becoming ever more crucial.