International assessments in a wide range of subjects are being prepared for and delivered through the medium of English in a variety of educational contexts. These assessments are taken by many candidates whose first language is not necessarily English. This raises important issues relating to assessment validity and fairness. This study describes an analysis of the linguistic demands in the Cambridge International General Certificate of Secondary Education (IGCSE)--a major high-stakes qualification for 16-year-olds. The focus of the study is IGCSE History, Biology, and Geography. Data for analysis includes syllabuses, question papers, mark schemes, and candidate performances. Findings suggest that each subject necessarily requires academic language (Cognitive Academic Language Proficiency) and some of the key academic language skills are identified. An average language proficiency level of B2 on the Common European Framework of References for Languages (CEFR) is useful to access typical IGCSE exams, and CEFR level of C1 could provide an added advantage of linguistic resources to be able to develop arguments needed for higher grades for Humanities subjects such as History and Geography. The outcomes have contributed to the question writing process and have informed the construction of a toolkit for content and language teachers.