Concerns over personal and communal security are as old as human societies, but as societies have changed arrangements for achieving and maintaining security have evolved accordingly. In this chapter we consider the implications of these changes for the governance of security. We begin with evolution of the institutions of security and associated linguistic developments and the debates that underlie them. We then turn to the issues of governance that have been central to these debates. We conclude by considering the challenges that contemporary forms of security provision present for the realization of the democratic governance of security. We explain how major transformations in the provision of security, and especially the allocation between states and the private sector for doing so, have occurred across the world during the last thirty years or so. Globalization and the impact of technological change during this period have placed much security provision outside the regulatory capacities of nation states, and adequate alternative forms and institutions of transnational governance have not yet been devised, nor have recent developments in thinking about how democratic governance is to be realized been reflected so far in discussion of such possible alternatives.