This comprehensive and accessible book is designed for use by students following the Theory of Knowledge course in the International Baccalaureate (IB) Diploma Programme. The book is also useful for students following other critical thinking courses. The fundamental question in Theory of Knowledge is 'How do you know? In exploring this question, the author encourages critical thinking across a range of subject areas and helps students to ask relevant questions, use language with care and precision, support ideas with evidence, argue coherently and make sound judgements. All chapters include the following features: - preliminary quotations to prompt critical thinking - questions and exercises to encourage students to actively engage with the material - reading resources to explore some of the topics in greater depth - illustrations to support the text Richard van de Lagemaat has more than 20 years' experience in international education.