This paper reviews the research on the impact of segregation on Latino and English Language Learner (ELL) students, including new empirical research conducted in Arizona. It also reviews court decisions regarding students' rights to be integrated with their mainstream peers, and provides data on the increasing segregation of Arizona's Latino and English learner students. Given that the great majority (over 80%) of Arizona's English Language Learners are Spanish speakers, there is considerable overlap between ELL and Latino students. This paper also reviews the extant literature on the impact of segregation at both the school and classroom levels and pays special attention to the particularly deleterious effects of linguistic isolation for English learners. The paper concludes that the excessive segregation of Arizona's Latino and EL students is most probably harmful to these students' achievement and social and emotional development and that there are alternative strategies that the state could use to ameliorate these harms and provide a more effective education for these students. (Contains 80 footnotes and 1 chart.)