Drawing on insights emerging from studies of the cellular networks formed by fungi, this book describes the fundamental indeterminacy that enables life forms to thrive in and create inconstant circumstances. It explains how indeterminacy arises from counteraction between associative and dissociative processes at the reactive interface between living systems and their surroundings. It stresses the relevance of these processes to understanding the "dynamic contexts" within which living systems of all kinds - including human societies - explore for, use up, conserve and recycle sources of energy. By focussing on dynamic boundaries, the book counterbalances the view that living systems are "assembled" entirely from building-block-like units - individuals and genes - that can "freely" be sifted, as opposed to "channelled", by natural selection. It also shows how the versatility that enables life forms to proliferate in rich environments, whilst minimizing losses in restrictive environments, depends on capacities for error and cooperation within a fluid, non-hierarchical power structure.