Thinking, particularly reflective thinking or inquiry, is essential to both teachers’ and students’ learning. In the past 10 to 15 years numerous commissions, boards, and foundations as well as states and local school districts have identified reflection 0 inquiry as a standard toward which all teachers and students must strive. However, although the cry for accomplishment in systematic, reflective thinking is clear, it is more difficult to distinguish what systematic, reflective thinking is. There are four problems associated with this lack of definition that make achievement of such a standard difficult. First, it is unclear how systematic reflection is different from other types of thought. Second, it is difficult to assess a skill that is vaguely defined. Third, without a clear picture of what reflection looks like, it has lost its ability to be seen and therefore has begun to lose its value. And finally, without a clear definition, it is difficult to research the effects of reflective teacher education and professional development on teachers’ practice and students’ learning. It is the purpose of this article to restore some clarity to the concept of reflection and what it means to think, by going back to the roots of reflection in the work of John Dewey. I look at four distinct criteria that characterize Dewey’s view and offer the criteria as a starting place for talking about reflection, so that it might be taught, learned, assessed, discussed, and researched, and thereby evolve in definition and practice, rather than disappear.