Starting from 1990, Corpus of Contemporary American English (COCA) picks 20 million words of English language each year, which contains more than 500 million words at present. Based on COCA, this series of Step by Step Towards Core Vocabulary of English offer 4 levels of English vocabulary: Elementary, Intermediate, Upper-intermediate, and Advanced, grouped in 1,000 words and reaching ultimately to 17,000 most frequently-used English words. 3,000 Elementary Words---Most Basic English Words 4,000 Intermediate Words---For Intermediate Learners 4,000 Upper-intermediate Words---For High School Students, TOEFL, IELTS 6,000 Advanced Words---For SAT, ACT, GRE, GMAT . CLICK HERE TO START DOWNLOAD