The Handbook of TESOL in K-12, First Edition. Edited by Luciana C. de Oliveira. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd. Throughout the world, many students are educated in a language other than their home language. This is especially prevalent in English‐speaking countries such as Australia, Great Britain, Canada, and the United States, which have a tradition of receiving immigrants in their schools. Educators working with these second language (L2) learners have been concerned for some time with the need to develop language that goes beyond everyday use. Cummins (1979) first proposed a distinction between basic interpersonal communicative skills (BICS) and cognitive academic language proficiency (CALP). Later the notion of language‐based content learning or content‐based language learning (Crandall, 1987; Mohan, 1986) emerged. Since the turn of the 21st century, there has been an explosion of studies investigating what is referred to as the language of schooling (Schleppegrell, 2004), academic English (Bailey, 2007), academic language (AL) (Gibbons, 2009; Zwiers, 2008), and disciplinary linguistic knowledge (Turkan, de Oliveira, Lee, & Phelps, 2014). Concern for language and literacy development in education is reflected in such reforms as the one pro- moted by the British educational system (Chen, 2007), the Common Core State Standards (CCSS, 2010) and the Next Generation Science Standards (NGSS, 2013) in the United States and The Australian Curriculum, Assessment and Reporting Authority (ACARA, 2012). In addition, language specific standards such as WIDA (World‐class Instructional Design and Assessment) English Language Development Standards (2013) and TESOL (Teaching English to Speakers of Other Languages) Pre‐K‐12 English Language Proficiency Standards (2006) have added to the focus on AL instruction and proficiency. Overview of Issues and Approaches The concept of AL has drawn attention and controversy since Cummins (1979) suggested the distinction between BICS and CALP. This chapter reviews various definitions and scope of what is considered AL. It explores what the research says with respect to the importance of implementing the concept to education. Opposing positions which stress the impor- tance in education and those who claim a negative impact on marginalized student populations are briefly presented. A Developmental and Contextual Perspective on Academic Language MARíA ESTELA BRISK AND ZHONGFENG TIAN 4