This document provides information about the 4000 Essential English Words book series. It discusses the selection process for the vocabulary words, which were chosen based on frequency analysis of English course materials. It notes that the words cover a large proportion of words found in newspapers, academic texts, novels, and conversations. It describes the learning activities in the books and how they are designed to reinforce word meanings and usage. It concludes by recommending additional activities like flashcards and graded readers to further support vocabulary learning outside of the classroom.