History and methods of epidemiology, the study of disease patterns. It starts by detailing the work of early pioneers, such as John Snow, who linked cholera outbreaks to contaminated water, and Florence Nightingale, who demonstrated the importance of sanitation in preventing disease. The text then examines various types of epidemiological studies, including observational and experimental approaches. It emphasizes the importance of distinguishing between common-source spread, where infection originates from a single source, and propagated spread, which occurs through person-to-person contact. The text further discusses different modes of transmission, including contact, vehicle, and vector transmission, and how these mechanisms contribute to the spread of infectious diseases. Finally, the text delves into the challenges presented by emerging and reemerging infectious diseases, highlighting the need for continuous monitoring, research, and global collaboration in public health efforts.