Complexity is all around us now to the point where practitioners across many fields must engage with it. But complexity comes with uncertainty, ambiguity and contradiction that makes it arcane on first encounter. Of all the theories surrounding complexity, hierarchy theory is the most intuitive and tractable because hierarchies and levels are habitual parts of human thinking. Hierarchies are associated with shifts across scale. Engineers rescale as they must, but always work one level at a time so as to avoid collapse through emergence. By contrast rescaling to find new levels leads to a fundamental disconnect that requires hierarchy theory to chart the way across a multi-layered labyrinth. Hierarchy theory uses holons, which are simultaneously quasi-autonomous wholes while also being a part of some larger holon. Part-whole status is contradictory; suddenly conventional, familiar hierarchies are not so comfortable. Nonlinearity can curve so far as to introduce infinities that created new levels. Models have to be internally consistent, but in the contradictions of moves between levels narratives save the day by abandoning verity as an issue in favor of asserting a point of view. While normal science relies on linking models, hierarchies tell narratives which can be inconsistent but still powerful. Hierarchy theory investigates the role of the observer in complex systems. This book parses out the implications of all of that.