Though data-based (evidence-based) decision making has long been normative in science-based professions, it has never been an essential benchmark for effective practice in education. This situation began to radically change with the passage of the No Child Left Behind (NCLB) legislation in 2001. At the heart of this legislation is the belief that educational decision making at all levels should be evidence based to the extent possible. NCLB had (and continues to have) bipartisan political support and, although modifications to the original legislation are sure to occur, the belief in evidence-based decision making isn't likely to fade away. Education has fought long and hard to gain acceptance as a profession and, since professionals by definition use data to shape the decisions they make, education has little choice but to continue moving in this direction. This 42-chapter handbook will be a major contribution to the literature of education. It will be a comprehensive, cross-disciplinary, research-based, and practice-based resource that all educators can turn to as a guide to data-based decision making.