This document provides an introduction to health systems. It defines key terms like health, health care, and health systems. A health system is described as an economic system comprised of units, agents, and institutions that interact to adapt, adjust, and achieve coherence in relation to human health. The seven principal health systems are identified as primary health services, workforce, governance, financing, supply chain, information systems, and households. Dimensions for assessing health systems include output, stability, fairness, efficiency, protection, freedom, and innovation. Examples of institutions, adaptations, and coherence mechanisms within health systems are discussed.