A fair and valid assessment for every child, as mandated by legislation such as the No Child Left Behind Act (NCLB) of 2001 and the Improving America's School Act of 1994, must consider the complexity inherent in assessments for subgroups of students. Due to the rapid growth of the population of English language learners (ELLs) in the United States, and because of the confounding of language proficiency with content assessments of ELL students, issues concerning the assessment of these students deserve special attention. ELL students, relative to their non-ELL counterparts, are not performing as well academically, which has implications for their future success. This chapter is structured around a discussion of factors that potentially have a great impact on the equity and fairness of assessment for the ELL student population. These factors include: (1) the classification of ELL students; (2) inclusion/exclusion criteria; (3) the impact of language factors on the assessment of ELL students; (4) the use of test forms in different languages as an accommodation; (5) the appropriateness, validity, and feasibility of accommodations; and (6) cultural and other factors. These issues can have a significant impact on the authenticity of the accountability system for ELL students. The greater the impact of these factors on ELL student performance, the more the fairness of accountability systems is compromised.