Privacy matters because it shields us from possible abuses of power. Human beings need privacy just as much as they need community. Our need for socialization brings with it risks and burdens which in turn give rise to the need for spaces and time away from others. To impose surveillance upon someone is an act of domination. The foundations of democracy quiver under surveillance. Given how important privacy is for individual and collective wellbeing, it is striking that it has not enjoyed a more central place in philosophy. The philosophical literature on privacy and surveillance is still very limited compared to that on justice, autonomy, or equality-and yet the former plays a role in protecting all three values. Perhaps philosophers haven't attended much to privacy because for most of the past two centuries there have been strong enough privacy norms in place and not enough invasive technologies. Privacy worked for most people most of the time, which made thinking about it unnecessary. It's when things stop working that the philosopher's attention is most easily caught-the owl of Minerva spreading its wings only with impending dusk. With the spread of machine learning, a kind of AI that often uses vast amounts of personal data, and a whole industry dedicated to the trade of personal data becoming one of the most popular business models of the 21st century, it's time for philosophy to look more closely at privacy. This book is intended to contribute to a better understanding of privacy from a philosophical point of view-what it is, what is at stake in its loss, and how it relates to other rights and values. The five parts that compose this book respond to five basic questions about privacy: Where does privacy come from? What is privacy? Why does privacy matter? What should we do about privacy? Where are we now?