The Theory of Knowledge programme is central to the philosophy of the International Baccalaureate. It encourages students to question the basis of knowledge and to develop the ability to evaluate critically information from a wide variety of sources. Students are used to being given facts that they are expected to learn but in this course they are expected to question the knowledge iself - what do I know, how do I know and is it likely to be true or not? This book provides an introductory framework that looks at ways to approach these and other questions. It covers ways to look for answers and highlights the problems that arise when we do so. As a result, we find that some questions have definite answers, while others seem too difficult to answer by reason or experiment. To encourage this critical thinking the "Pupil's Book" also includes a wide range of material from other sources to stimulate discussion.