Ideas about information are pervasive, yet the fundamental nature and structure of information - if indeed it has one! - remains elusive. Work done from many different perspectives, including those of physics, biology, logic, computer science, statistics, and game and decision theory, has yielded insights into various aspects of information. Could there be a comprehensive, unified theory? We shall chart a particular path, focusing on the idea of *information flow*, and show how common mathematical structures arise in the description of information flow in computer science, logic and quantum information.