The educational research community has made great strides in clarifying and enhancing our understanding of professional development and how it occurs. Yet in relation to one question--How do people develop professionally?--this knowledge base falls short, for while much research has been directed at addressing the question, findings have tended to lack the specificity that offers the kind of elucidation that may usefully inform professional development-focused leadership policy and practice. In particular, the micro-level cognitive process of professional development--what occurs inside an individual's head in order for her/him to experience a professional development "episode"--remains under-examined in educational research. This article makes a contribution towards addressing this short-fall. It presents the author's conceptual analyses of professionalism and professional development--revealing the multidimensional componential structure of each--and examines how understanding of this multidimensionality may help school leaders promote and facilitate professional development.