This article addresses how 'powerful' curriculum theory might be constructed from the perspective of the German "Didaktik" tradition--highly compatible with Schwab's the Practical. To start with, I scrutinize Joseph Schwab's model of curriculum planning and Wolfgang Klafki's model of lesson preparation and examine two theories of content that underpin the two models. Invoking the German "Didaktik" tradition, I next explicate a distinctive form of theorizing that yields powerful curriculum/"Didaktik" theory. I argue that "Didaktik," together with the Practical, provides a viable way of constructing powerful curriculum theory--exemplified by a theory of knowledge and a theory of content--in the current context. I conclude by drawing implications for our understanding of the powers of professional educational knowledge and for tackling the current crisis in educational theory.