States participating in the four federally-funded assessment consortia are required to establish a "common definition of English Learner." This includes the two Race to the Top academic assessment consortia and the two Enhanced Assessment Grant English language proficiency (ELP) assessment consortia. This paper provides guidance that consortium member states can use to move toward establishing a common English learner definition in ways that are theoretically-sound, evidence-based, pragmatic, and sensitive to the many policy, technical, and legal issues. Specifically, the paper briefly outlines central issues, and discusses policy and technical options, for defining English learners using a four-stage framework of key criteria and processes to: (1) Identify a student as a "potential" English learner; (2) Classify (confirm/disconfirm) a student as an English learner; (3) Establish an "English-language proficient" performance standard on the state/consortium ELP test against which to assess ELs' English-language proficiency; and (4) Reclassify a student to former-EL status through the use of multiple exit criteria. Appended are: (1) Common English language proficiency performance descriptors based on an amalgamation of descriptors from CA, AZ, TX, and the WIDA Consortium; and (2) Methods for Establishing an English Language Proficient Performance Standard