What does "illness" mean? And what about "health"? Although these concepts are fundamentally important for practical questions of healthcare—such as regulating access to solidarity-funded medical services—they are rarely the explicit subject of societal debate. This volume brings together modern classics of the interdisciplinary discussion on the concepts of illness and health. It first presents the current state of philosophical discourse, then introduces theories that understand health not merely as the absence of illness, and finally focuses particularly on the concept of mental illness. The aim of this volume is to bring an impactful debate closer to a broad audience.