The U.S. Department of Education (USED) requires states participating in either of the two Race to the Top assessment consortia (Smarter Balanced Assessment Consortium and Partnership for Assessment of Readiness for College and Careers [PARCC]), as well as those participating in either of the two Enhanced Assessment Grant (EAG) English language proficiency assessment consortia (WIDA's Assessment Services Supporting English Learners through Technology Systems [ASSETS] and CCSSO's English Language Proficiency Assessment for the 21st Century [ELPA21]), to establish a "common definition of English Learner." Specifically, each consortium "must define the term in a manner that is uniform across member states and consistent with section 9101 (25)1 of the ESEA" (US Department Of Education, 2010, p. 20). Although the two consortia developing alternate assessments based on alternate achievement standards (AA-AAS) are "not" required to develop a common definition of English learner (EL), their member states largely overlap with these assessment consortia and they will include their English learners in these assessments. Having a common EL definition that agrees with the definition adopted by the other consortia is clearly desirable, if not essential. As discussed in this paper, this requirement presents substantial challenges that will call for a carefully coordinated, multiyear effort within and across consortia member states. The effort will need to proceed in stages and encompass several critical decisions. Since the federal definition of English learners posits that their level of English language proficiency (ELP) may deny them the ability to perform proficiently on academic content assessments, a relationship between students' ELP and content assessment results must be established. Recently developed empirical methods illustrate how this might be done. However, this requires operational data from all consortia assessments. Since assessment scaling and academic content performance standards across states and consortia are needed to conduct such empirical analyses, scaling and standard-setting for all assessments would first need to be completed. Very likely, changes to state policy and regulations will also be required, which implies potential legislative or state board of education action. Some key issues and opportunities are highlighted. (Contains 10 footnotes.)