This article systematically reviews the cost study literature as it relates to the treatment of English language learners (ELLs). Despite the substantial number of costing out studies that have been conducted over the past several decades, the school finance literature has failed to focus on ELLs--the fastest growing segment of the school-age population. Little attention has been paid to how ELL students are treated under the various costing out methodologies or which approaches yield the most useful results. The two criterion to select the costing out literature to review included (a) peer-reviewed journal articles and commissioned reports that used one of the four primary cost study methodologies (professional judgment panel, successful school model, evidence-based model, and cost function analysis), and (b) studies published after 1990 that focused on generating statewide funding recommendations at the district level. A total of 70 empirical cost studies met these criteria. The review concludes that there is substantial variability in the treatment of ELLs across cost study methodologies, although all methods agree that current funding levels are insufficient to meet specified performance standards. To comprehensively assess the resource needs of this growing school population, cost studies that specifically focus on ELLs will need to be conducted to improve transparency and representativeness for ELLs. (Contains 6 tables and 4 notes.)