While populations in developing countries continue to suffer from old infections such as tuberculosis, HIV and malaria, developed nations are battling chronic diseases and new health challenges such as lifestyle risk behaviours and the high prevalence of overweight and obesity (World Health Organization, 2008). The constantly changing environment, increased international travel and globalisation, and social, economic and political changes have contributed to the changing nature and patterns of disease and health issues. To better address the complex interrelationships among various determinants and health/illness outcomes, multidisciplinary efforts are required to protect and promote population’s health. Epidemiology is one such discipline in public health. No matter which specific career in public health a student eventually develops, the knowledge and skills involved in epidemiology will be useful. Its approach to critical thinking and problem-solving forms the basis for evidence-based decision-making in the health sciences as well as for health intervention research. Epidemiology uses quantitative methods to collect and analyse data to investigate disease occurrence and possible causes of disease in order to find solutions to health problems in different populations. A commonly cited definition of epidemiology as ‘the study of the distribution and determinants of health-related status or events in specified populations and application of this study to control of health problems’ (Porta, 2008, p.65) has clearly outlined the purpose, the use and the applications of epidemiology. This chapter introduces the basic concepts in and use of epidemiology, the common epidemiological study designs and the quantitative measures used to describe the health status of populations and identify potential determinants of ill health. The chapter also draws examples of international and Australian research and health data to strengthen the theoretical concepts and principles introduced in this chapter.