First paragraph: The purpose of this chapter is to set out what happens when a teacher undertakes a professional enquiry in a classroom. Professional enquiry follows a cycle that is used as the basis of both action research and experiential learning. Here, we keep both of these aspects of enquiry in mind and describe the content and process of professional enquiry: content a focus on a particular aspect of pupils’ learning and an experiment, in the form of an intervention, to improve pupils’ skills and understanding in relation to this chosen area – and process a pattern of actions, underpinned by a set of principles, whereby both teacher and learners change their practice and their relations as part of a joint learning experience. We shall use an account of a classroom-based enquiry carried out in a primary school as part of the process of working towards the award of Chartered Teacher status to illustrate the major stages of conducting an enquiry. Each of these stages is examined in detail and linked to other experiences of undertaking classroom enquiries