This exploratory study is an attempt to shed light on the internal dynamics of secondary teachers' and academics' professional learning, its context and its occasions, in a course of a university-provided in-service professional development programme in Greece, using the experiences and perceptions of its participants. In investigating the above, the study harnesses a qualitative methodology and a research framework that draws upon a set of ideas that cohere under the rubric "programme development," in order to generate a heuristic that guides research techniques and analysis procedures. The investigation reveals professional learning to be characterised by a number of dimensions: professionality, mutuality, emotionality and formality. Professional learning is therefore seen as a complex process rather than linear, a step-by-step event. The article concludes by emphasising a shift from the delivery of the in-service courses to an understanding of the complexity of the processes by which professional learning is developed.