This chapter explores case-control studies, an analytical observational design particularly suited for investigating rare diseases and conditions with long latency periods. The methodology is explained, with cases defined as individuals with the outcome of interest and controls as those without, drawn from the same source population. Retrospective assessment of exposure history forms the basis of analysis, allowing researchers to identify associations between exposures and outcomes. The odds ratio is introduced as the principal measure of association, with guidance on its interpretation and limitations. The chapter highlights the efficiency of case-control studies, requiring smaller sample sizes compared with cohort designs, and their particular value when incidence data are difficult or costly to obtain. Challenges such as recall bias, selection bias, and difficulties in establishing temporality are critically discussed. Strategies to minimise bias, including careful matching of cases and controls and validation of exposure measures, are outlined. Practical examples demonstrate the application of case-control studies in fields such as cancer epidemiology and outbreak investigations. The chapter concludes by emphasising the continued relevance of case-control designs in modern epidemiology. This chapter maps to syllabus section 3.2.3, which requires detailed knowledge of case-control studies, their strengths, weaknesses, and potential biases.