This chapter presents an account of how research on the development of mathematical thinking has been applied to the practice of mathematics education. The chapter first offers a brief history of the field and then gives a summary of key aspects of contemporary research. Next, the chapter turns to a discussion of three applications: (a) mathematics textbooks, (b) teacher development, and (c) techniques of assessment. The chapter ends with a discussion of the ways in which research gets translated into practice; a reflection on both the power and the limitations of contemporary research for purposes of application; and a proposal concerning the vital role that psychological research should play in the education of teachers, which is arguably one of the key problems--if not the central problem--of American education. (PsycINFO Database Record (c) 2012 APA, all rights reserved)