4000 Essential English Words is a six-book series that is designed to focus on practical high-frequency words to enhance the vocabulary of learners from high beginning to advance levels. The series presents a variety of words that cover a large percentage of the words that can be found in many spoken or written texts.
Each unit includes 20 target words with several learning exercises that learners can use to practice vocabulary. Also, I was happy to see that the book uses the target words in a reading passage