Present-day society is often referred to as a knowledge society. But how can knowledge be defined and what role does it play, along with the related or connected concepts of learning and media/ICT? In what sense does learning lead to knowledge, what forms of learning are adequate in the so-called knowledge society, and how are appropriate forms of learning underpinned? How should media be conceptualised, and what is the role of the media, not least digital media, i.e. ICT, in society? Most people seem to agree that we live in a "knowledge society". But what is knowledge, and how can knowledge be categorised? How does learning and life-long learning help us making "knowledge society" a reality, and what is the role of e-learning? The book aims at answering all these basic questions. It provides a definition and logical categorisation of knowledge. It categorises learning and teaching in a similar system. It analyses media education, media socialisation, and the use of digital media in and for teaching. It summarises the main theories of e-learning. And it presents the German sociologist Niklas Luhmann's theory of the educational system. The book is written for everybody who works professionally with education, knowledge and knowledge management, including educational researchers, e-learning specialists, teachers and students at teacher training colleges - and for everybody interested in understanding the so-called knowledge society.