A quarter century ago, the National Council of Teachers of Mathematics (NCTM) published the first Handbook of Research on Mathematics Teaching and Learning (Grouws, 1992); 15 years later, they published a Second Handbook of Research on Mathematics Teaching and Learning (Lester, 2007). Now, in anticipation of its centenary in 2020, NCTM has published the Compendium for Research in Mathematics Education. The replacement of Handbook of by Compendium for in the title, though originating as an issue associated with copyright permission, also represents a kind of progress. The word handbook was originally used to mean something like “small, easily consulted pocket reference,” which certainly did not apply to the first two publications. In his preface, Cai quotes the dictionary definition of compendium as “‘a collection of concise but detailed information about a particular subject’ that has been ‘systematically gathered’” (p. vii), and he emphasizes that the three components of “concise,” “detailed,” and “systematically gathered” characterize the compendium at hand. Perhaps even more significant is the change from of to for. That change was made, according to Cai, to signal a shift from a static, backward-looking collection of observations about research in our field to a resource that could be used to move that research forward. To service that shift, the authors of all the compendium chapters were asked to speculate on future directions for research in light of the research they were reviewing.