This research compiled two corpora, one for English-medium textbooks for business core courses (totaling 7.2 million running words) and the other for business research articles (7.62 million tokens), to form a basis of analysis. The results show that knowledge of the most frequent 3500 word families and 5000 word families plus proper nouns would provide 95% lexical coverage of a business textbook and a business research article respectively. Business textbooks reached 98% coverage at the 5000 word level while business research articles reached 98% coverage at the 8000 word level. Among the textbooks across 12 business subject areas, production & operation (involving the 3000 word level necessary for minimal comprehension at 95% lexical coverage and the 4000 word level necessary for adequate comprehension at 98% coverage) was the least vocabulary-demanding, while business policy & strategy (covering 95% at the 5000 word level and 98% at the 7000 word level) was the most vocabulary-demanding. Excluding business policy & strategy and management information systems which showed the greatest variation, the vocabulary levels of research papers entailing different specialist knowledge were mostly within the range of 5000 word families (at 95% coverage) and 8000 word families (at 98%). (Contains 6 tables.)