This article provides Learning Forward's definition of professional development. Learning Forward is seeking legislative amendments to include its definition in the Elementary and Secondary Education Act as reauthorized by the No Child Left Behind Act of 2001. These amendments will clarify what practices qualify for federal, state, and district funding, while stating that professional development needs to directly impact a teacher's classroom practices and student achievement. This article presents and discusses the key points in Learning Forward's definition of professional development: (1) fosters collective responsibility; (2) primarily occurs several times per week; (3) continuous cycle of improvement; (4) provides job-embedded coaching; and (5) may be supported by external assistance.