Twenty years ago, this journal, which was then called JSD, was my first introduction to the unique considerations involved in evaluating professional learning. I was struck by how field leaders like Hayes Mizell, Joellen Killion, and Thomas Guskey provided guidance so elegant that the complex process of program evaluation seemed straightforward and almost natural. Of course, elegance only looks easy. You’d be hard pressed to find a professional learning leader who would call evaluation easy, even among the experts named here. That’s why we still need guidance on how to do it and why we continue to hear impassioned calls to use the best methods available to fortify the evidence base. As I’ve reread many years’ worth of articles and books, I have seen the