School middle leadership has become an important focus of attention for research and development. This paper reports on two reviews of empirical research into the nature of posts of responsibility held by teachers in secondary schools who are not regarded as part of the senior school management team. Empirical studies in the English language published between 1988 and 2005 were systematically reviewed. The authors found that two key tensions were identified repeatedly in the literature: between expectations that the middle leader role had a whole-school focus and their loyalty to their department, and between a growing culture of line management within a hierachical framework and a professional rhetoric of collegiality. Three key issues ran through these tensions: issues associated with the concept of collegiality; questions around the concepts of professionality, authority and monitoring; and questions of authority and expertise. A range of factors influencing middle leaders' attitudes to their role are discussed, and the possibility of analysing these through institutional theory and structure-agency duality is discussed.