Theory of Knowledge textbooks
Theory of Knowledge (TOK) is one of the IB Diploma Programme requirements, along with the Extended Essay and CAS (Creativity, Action, Service). Both Oxford and Cambridge have TOK textbook offerings, and both are excellent, with plenty of examples, scenarios, and thought-provoking questions to help students engage with the course.
Note that a new TOK syllabus will be taught starting from August 2013 (ready for 2015 examination) and at present (July 2013) only two of the textbooks here cover this new syllabus.
This newly released book is written specifically for the latest (first teaching 2013) syllabus, and covers the new TOK Areas of Knowledge, Ways of Knowing, and the increased emphasis on group and personal knowledge.
This new edition is ready for the new TOK syllabus (first taught August 2013), which really makes it the only recommended TOK textbook at the moment.
This book is not widely available yet, but Book Depository is a good option for non-US customers as they offer free worldwide shipping.
Note that this textbook does not cover the new TOK syllabus (which will be first taught in August 2013 for May 2015 examination). This means it does not cover the changes to the course, including the new Ways of Knowing.