The ‘civilian control’ model of police complaints systems is premised on a clear separation between ‘civilian-led’ and ‘police-led’ investigative processes. This paper examines the nature of ‘civilianness’ in civilian control-based oversight agencies by examining the cultural profiles and internal dynamics of three police oversight bodies within the British and Irish islands. Based on over 100 interviews, it presents findings relating to the motivations behind oversight work and the dynamics associated with the joint workings of investigators with both non-police and police backgrounds. It concludes that civilian control may be seen as a differentiated space with varying degrees of civilianness, including remnants from and continuities with police culture.