Oxford Bookworms offer students at all levels the opportunity to extend their reading and appreciation of English. There are six stages, taking students from elementary to advanced level. At the lower stages, many of the texts have been specially written for the series, to provide elementary and lower-intermediate students with an introduction to real reading in English. At the higher stages, most of the books have been adapted from works originally published for native speakers. The language controls used in Oxford Bookworms are based on a syllabus specially created for the series by Tricia Hedge. This takes account of the more traditional approaches to grading and recent research into the nature of reading difficulty. The approximate vocabulary count for each stage is: Stage 1 - 400 words; Stage 2 - 700 words; Stage 3 - 1000 words; Stage 4 - 1400 words; Stage 5 - 1800 words; Stage 6 - 2500 words. All stages have exercises for classroom or private use, plus a supporting glossary to help students with vocabulary. Illustrations are used, especially at the lower stages, to help comprehension.