This study maps key features of effective Teacher Professional Development (TPD) and the framework of Communities of Inquiry (CoI), in an effort to gain an understanding of how these features contribute to teachers’ collegial learning. Activity system, as described by Engeström (1987)/(1999), is used as a theoretical lens which allows for the visualization of TPD as a complex system. The result indicates that, apart from differences in the level of detail in the description of various features, there are differences in the demands the two models place on teachers. Establishing norms that promote collegial learning, in which critical inquiry is expected, emerged as a critical issue. This highlights the importance of viewing any variant of TPD as a process, in which the functions of features shift. Awareness of this process may prove important in designing and implementing future TPD initiatives.