This chapter looks at how beginning teachers construct their professional knowledge how they learn to become teachers. It explains how teachers develop their professional understandings. More specifically, It considers some of the central ways in which researchers and theorists have viewed knowledge and put forward his own model of teacher identity as an alternative to traditional models of teacher learning. The modern era of research on teacher learning began about forty years ago with a new focus on teacher cognition. Adult learning, becomes the process of examining what understandings of the world you are actually relying on and making conscious decisions about whether to retain, jettison, long-held views. It's also sometimes criticized for being dominated by society's prevailing norms, ideological prejudices, or naive opinions. Uppercase Theory is sometimes criticized for being too abstract, rarefied, or full of soaring generalities.