No Child Left Behind (NCLB), the reauthorization of the Elementary and Secondary Education Act, was passed in 2002. This legislation broadly states federal policy regarding education and is situated within the historical context of Lyndon Johnson's Great Society programs. Like any federal legislation, NCLB consists of the legislation itself but also the procedures established by the U.S. Department of Education and interpretations of the legislation at the local education-authority level. The author describes two of the four pillars of the legislation most relevant for evaluators: accountability requirements and application of rigorous scientific research. With the impending reauthorization of NCLB, possible changes to the legislation are discussed.