This review of the current literature on second language learning was to inform the following four questions: (1) what are the effects of learning a second language on the first language? (2) What is the role of content instruction in offering a second language? (3) What are the effects of learning a second language on students with special needs? (4) What are the effects of learning a third language on students for whom English is a second language? And, they were to look at the overview for the challenges and benefits for those who are learning a second language. The range of literature surveyed is very broad. Academic journals, books, conference proceedings, technical reports and online materials were consulted. Findings include: (1) Exposure to a second language can: enhance the complexity of first-language syntax used; enhance language use skills; enhance non-linguistic skills; Acquiring knowledge in a second language does not impede the ability to access that knowledge in the first language; (2) Numerous models of content-based language programs exist, each illustrating a different balance between content-area and second-language learning outcomes. Student second-language proficiency levels, the nature of the content material and the amount of time devoted to the program all need to be considered in choosing an appropriate model for any given context. In terms of language learning, content-based language teaching is a time-efficient and effective way of promoting the development of general second-language skills; (3) There is a great deal of research that looks at the difference between students who are culturally and linguistically diverse versus those with disabilities. In sum, all of this research looks at how to assess students in second-language classrooms; how to teach students with special needs in second-language classrooms; and problems related to specific concerns such as dyslexia, word recognition, learning disabilities and differences between learning a first language and learning a second language; and (4) The acquisition of a third language is a common occurrence around the world. Learning a third language is aided by proficiency in the first language, and acquired skills can be transferred among the languages spoken. Students for whom English is a second language may benefit from third-language acquisition, depending on the model of instruction. [This document was prepared by The Language Research Centre (LRC) of the University of Calgary.]