The experience of socialisation for those new to headship can be challenging and often traumatic (Crow, 2007). Research into the socialisation of new headteachers is not extensive and has primarily been concerned with identifying and ordering stages in the socialisation process, for example, phases of headship. Such an approach neither allows for an analysis of the complexity of socialising influences nor does it enable the generation of explanatory theories. The purpose of the current research was to provide an understanding of the socialisation of new headteachers from an analysis of significant socialising experiences. The aims of the research were to: 1.analyse the socialisation of new primary headteachers from a role boundary perspective. 2.test the suitability of the role boundary concept as a rigorous, theoretical and methodological tool that can be applied to researching the field of headteacher socialisation. The research analysed critical incident vignettes from the experiences of seven newly appointed primary school headteachers up to their first three years in post. Data was collected using two research methods; semi-structured interviews and a written log. Twenty two critical incident vignettes were analysed using an interpretive methodology underpinned by an analytical framework based upon the concept of role boundary. The role boundary is described as being the point of delineation between a set of behaviours that are considered to be legitimate in role and those behaviours that are considered illegitimate in role. The role boundary concept allows for an analysis of the socialising experiences of new headteachers as they and the organisation engage in a recurrent, reciprocal and relational socialising process that seeks to establish those behaviours that are, and those that are not, legitimately enclosed by their role boundaries. The research found that socialisation is the process by which the new headteacher and the organisation seek to establish and position their respective role boundaries. Headteachers experience socialisation as a series of emotionally challenging interactions where the central purpose is to establish who has the legitimate authority to take decisions and to take actions in the following three main areas; task role allocation, resource allocation and the creation and application of organisational procedure. These interactions are immediate, are intense and have the potential to lead to conflict where individuals contest the limits of their respective role boundaries. The research finds the concept of role boundary as a theoretical and methodological tool to be of heuristic and analytical value in understanding and explaining headteacher socialisation and presents a role boundary socialisation theory to explain the dynamics of the socialisation process.