This document provides an overview of basic epidemiology concepts including the difference between illness and disease, models of disease and illness, the natural history of disease, and types of disease occurrence. Key points include: illness refers to feelings of discomfort without an identifiable cause, while disease refers to a condition where the body is not working properly; common models of disease include biomedical and biopsychosocial; the natural history of disease involves stages of susceptibility, pre-symptomatic disease, clinical disease, and recovery or death; and diseases can be infectious, chronic, or genetic in nature.