Frequent statements are now made in the medical and public health literature about an imminent revolution in health care, preventive medicine and public health driven by the use of digital devices and associated apps, websites and platforms. However, it is important to adopt a more critical approach when assessing the impact and implications of digital health technologies and the data that they produce. Digital health technologies potentially generate different ways of thinking about, practising and experiencing medicine, healthcare and public health. From a perspective that is informed by critical social and cultural theory, these changes have the potential to challenge entrenched conceptualizations and experiences of illness, health, disease and medical care and practice. Following an overview of the range of digital health technologies that are currently in use, this chapter focuses on the digital data that are generated from these technologies, discussing the implications for the digital knowledge economy, data security and privacy, social inequalities and civil rights.