Epidemiology is the science that studies the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and informs policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare. In this course we will discuss the basic principles of epidemiology and the underlying methodological and statistical principles. In an in-class experiment, we will study the spread of an infectious disease. Based on data from literature, we will analyse worldwide distribution of pneumococcal disease and trends in obesity.