This book arose as an attempt to collect and collate ideas and problems around notation that many of us have been dealing with on several levels. We have processes of varying complexity, we would like to work out ways to discuss them that move beyond the dichotomy of hand-waving or looking at the deepest level of code. We had many questions: In an interactive situation, how do we discuss the possibilities for interaction and the way a media should be playing, given the actions of visitors? How do we investigate the inner workings of an experience to see whether it makes sense, without building it completely in advance? We want to think of notation as an abstraction, a simplification, and intuitive or studied way of writing something down that succinctly summarises the important points of a given situation, process, object or system? This book and its ideas should help us think, discuss, design, build, analyse and document the systems.