The Every Student Succeeds Act of 2015 mandates that English language proficiency (ELP) standards align with content standards. As the fast-growing population of English learners (ELs) is expected to meet college- and career-ready content standards, the purpose of this article is to highlight key issues in aligning ELP standards with content standards. The overarching question is how to align ELP standards with academically rigorous and language-intensive disciplinary practices of content standards while respecting and maintaining the nature of the discipline within each area. I begin by describing contributions and shortcomings of content standards and ELP standards. Next, I propose consideration of three components in aligning ELP standards with content standards: (a) norms of disciplinary practices across content areas, (b) developmental progressions of disciplinary practices across K-12 grade levels or bands and across content areas, and (c) language use across levels of English proficiency. For each component, the challenges in establishing alignment and potential trade-offs in addressing these challenges are discussed. Finally, I highlight how these challenges present opportunities for substantive collaboration between EL education and content areas to move these fields forward and ensure ELs achieve academically rigorous content standards while developing ELP.