The population of school-aged English language learners (ELLs) has consistently and significantly increased over the past decade, transforming U.S. public schools, instruction, and teacher preparation. This digest discusses the need for increased numbers of teachers of ELLs and the particular linguistic and academic characteristics of ELLs. It focuses on: teacher supply and demand (the need for teachers of ELLs is particularly acute, and while percent of U.S. teachers have taught ELLs, less than 13 percent have received any training or professional development in the area); requirements for preparing teachers of ELLs (bilingual education, English as a Second Language, and mainstream education); and addressing the need (several organizations have developed standards to delineate what teachers of ELLs should know and be able to do, and these standards include such elements as proficiency in two languages, understanding of the impact of students' cultures on their learning, and assisting students in the development of their language abilities). The digest concludes that efforts are now being concentrated in the implementation of programs that incorporate the elements of effective preparation and professional development of teachers of ELLs. (Contains 14 references.) (SM)