This document provides an introduction to key concepts in public health including definitions, major issues, and the history of public health. It discusses how public health differs from clinical medicine by focusing on populations rather than individual patients. Public health aims to prevent disease and injury through community-level interventions and policy changes. The document also summarizes a famous case study where the physician John Snow used epidemiological methods to identify contaminated water as the source of a cholera outbreak in London in the 1850s.