Health systems have developed at different speeds, and with differing degrees of complexity throughout the twentieth century, reflecting the diverse political and social conditions in each country. Notwithstanding their diversity, all systems, however, share a common reason for their existence, namely the improvement of health for their entire populations. To attain this goal a health system undertakes a series of functions, most notably, the financing and delivering of health services. Since available resources are limited, delivering health services involves making decisions. Decisions are required on what interventions should be offered, the way the health system is organized, and how the interventions should be provided in order to achieve an optimal health gain with available resources, while, at the same time, respecting people’s expectations.