The major part of William's Words in Science is a dictionary of over 13,000 words and phrases that pupils meet in their first three years of secondary school (with directions to homophones or alternative spellings). There are also biographies of over 150 people who have been most influential in developing the ideas of science. The two other sections are a compilation of the important information that a pupil (and a teacher) needs, but can not always remember; and a summary of over 50 of the most important ideas in science, including diagrams such as the skeleton, body organs and the cycles of carbon, nitrogen, rocks and water.