The term "evidence-based programs" is becoming quite common in prevention and human service work. However, many still struggle to recognize the importance of evidence-based programs and to understand what qualifies as "evidence-based." The language used may even seem to confound the issue further. The terms evidence-based, research-based, science-based, blueprint programs, model programs, promising programs, and effective programs are often used interchangeably. Different agencies and groups have adopted different criteria to determine whether or not a program is evidence-based. In this fact sheet, the authors examine definitions of, and standards and reasons for using evidence-based programs. A list of evidence-based program web sites is also included. [This fact sheet was produced by the Prevention Research Center for the Promotion of Human Development.]