Despite the fact that the population of English Language Learners (ELLs) is rapidly increasing, there is ample evidence that indicates that most teachers can benefit from training for teaching ELLs effectively. The purpose of this study is to examine teachers' knowledge of instructional practices for ELLs, research on bilingual programs, research-based instructional strategies, and knowledge related to second-language development among 225 bilingual/English as Second Language (ESL) teachers in a large suburban school district in Texas. Additionally, because professional development (PD) plays a key role in teachers' knowledge, this study considers the PD opportunities provided to teachers of ELLs. Findings indicated that many teachers of ELLs are not receiving adequate training, particularly in areas related to bilingual education and knowledge related to second-language development, and that bilingual teachers are more knowledgeable than ESL teachers in terms of bilingual programs and knowledge related to second-language development. These findings have important implications for teacher PD.