Currently, many countries, including the Netherlands, are "plagued" by severe, both quantitative and qualitative, teacher shortages that are even expected to increase in the years to come. Teachers' occupational development, therefore, has become an important issue on the research agenda of the respective countries. It is essential to develop more thorough insights that enable human resource management (HRM) and human resource development (HRD) professionals in schools to take strategic decisions in developing teachers' professional development (TPD) and occupational expertise (OE). The aim of these strategic decisions is to cope effectively with shortages in this occupational sector. In this contribution, we propose a model that focuses on the influence of organizational and task factors on TPD which, in turn, is assumed to enhance OE. We will thoroughly discuss the so-called "TPD & OE model," and its implications for research and HRD practice. (Contains 4 figures.)