Textbook in PDF format This book adopts the logic of Systems Thinking and Control Systems, presenting a simple but complete theory called the Theory of Combinatory Systems. This new theory describes, interprets, explains, and simulates collective phenomena and their observable effects. Such collective phenomena – many of which are “one way", non-repeatable or reproducible – can all be described and understood using the model, as simple as it is general, of combinatory systems; that is, systems formed by collectivities, or populations of non-connected and unorganized individuals of some species, which appear to be directed by an invisible hand that guides the analogous actions of similar individuals in order to produce an emerging collective phenomenon