Sesame Subjects is a series of educational Sesame Street books, written by Kama Einhorn and published by Random House. To date, Christopher Moroney has illustrated six books in the series, while Joe Mathieu has illustrated two. Each book features Professor Grover as he helps Elmo and the reader (and sometimes a "special guest" character) to explore a different topic. Professor Grover uncovers facts and information about a range of subjects, from dogs and farms to vehicles and the senses. The series started in 2006 and new additions are continuing to be released regularly.