This book is about unsteady combusting flows, with a particular emphasis on the system dynamics that occur at the intersection of the combustion, fluid mechanics, and acoustic disciplines – i.e., on combustor physics. In other words, this is not a combustion book – rather, it treats the interactions of flames with unsteady flow processes that control the behavior of combustor systems. While numerous topics in reactive flow dynamics are “unsteady” (e.g., internal combustion engines, detonations, flame flickering in buoyancy-dominated flows, thermoacoustic instabilities), this text specifically focuses on unsteady combustor issues in high Reynolds number, gas-phase flows. This book is written for individuals with a background in fluid mechanics and combustion (it does not presuppose a background in acoustics), and is organized to synthesize these fields into a coherent understanding of the intrinsically unsteady processes in combustors.