"Penguin Readers" are graded at seven levels of difficulty, from "Easystarts" with a 200-word vocabulary, to Level 6 (Advanced) with a 3000-word vocabulary. In addition, titles fall into one of three sub-categories: "Contemporary", "Classics" or "Originals". At the end of each book there is a section of enjoyable exercises focusing on vocabulary building, comprehension, discussion and writing.