Broadly defined, evidence-based practice (EBP) is fundamentally about professional practice being informed and guided by best available evidence of what works. The EBP movement had its origins in the early 1990s in the United Kingdom in medicine and health care services. Sackett et al. defined evidence-based medicine as the "conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients. This practice means integrating individual clinical experience with the best available external clinical evidence from systematic research." This definition has pervaded the now wide-ranging EBP literature across many fields of practice, drawing on the idea of meshing research-based evidence with professional knowing and experience to make professional decisions and implement professional action. Interest in EBP has grown, and its application has extended from medicine to allied disciplines, such as nursing, pathology, and cardiology, and to the social sciences and business professions. Both the education and librarianship fields are developing strong approaches to EBP, and these provide directions, and pose challenges and tensions for EBP for school librarianship. Two characteristics stand out in the EBP frameworks being developed in education and librarianship: (1) using the best available evidence, which gives preeminence to evidence derived through randomized controlled trials; and (2) combining this evidence with professional acumen to deliver high-quality services. It is a question of evidence. The professional practice of school librarianship sits at the confluence of education and librarianship. Like evidence-based education, evidenced-based librarianship places emphasis on evidence-based decision making over opinion-based decision making, and on the conscientious interpretation and integration of research-derived evidence to shape and direct professional practice. What the EBP approach in school librarianship appears to make more explicit is not just the use of research-based evidence to make judgments and decisions about how to deliver the instructional and service roles of the school library to meet the goals of the school. The EBP approach to school librarianship also gives explicit attention to "user-reported evidence," that is, evidence of outcomes and impacts of professional practice based on student-generated evidence. (Contains 1 table.)