This thesis is an institutional ethnography of the Nigeria Police Force. It concentrates on evidence from 18 months of fieldwork in one particular police station, in the pseudonymised town of Dutsin Bature in central Nigeria, and draws comparative evidence from examples and locations elsewhere in Nigeria. The fieldwork evidence is also supported by analyses of public discourse, literature reviews, some formal interviews and historical research. The thesis aims to fill a gap in empirical scholarship by looking at policing in Nigeria primarily from the level of everyday practice, and deriving understandings of the ways the overall system works, rather than by taking normative structural approaches and basing suppositions of actual behaviour upon these. It also aims to document emic perspectives on policing in Nigeria, in contrast to most existing scholarship and public discourse which takes an external perspective, from which the voices and worldviews of police themselves are absent. The thesis situates this ethnography within three theoretical terrains. First, developing understandings of policing and public security in Africa, which have often neglected in-depth studies of formal police forces. Secondly, enlarging the ethnographic study of formal institutions in African states, to develop a closer understanding of what state systems are and how they function, beyond the overtly dysfunctionalist perspectives which have dominated recent scholarship. Thirdly, informing ongoing debates over state and society in Africa, problematising understandings which see these as separate entities instead of mutually constitutive, and drawing attention to the ways in which the two interpenetrate and together mould the public sphere. The thesis begins with a historical overview of the trajectory of formal policing in Nigeria, then examines public understandings and representations of policing, before moving inside the institutional boundaries, considering in turn the human composition of the police, training and character formation, the way police officers do their work in Dutsin Bature, Nigerian police officers’ preoccupation with risk and the systemic effects of their efforts to mitigate it, and finally officers’ subjective perspectives on their work, their lived realities, and on Nigeria in an era of transition. These build together to suggest some conclusions pertinent to the theoretical perspectives.