This chapter provides an overview of key measures of association used in epidemiology to quantify the relationship between exposures and health outcomes. It covers the calculation, interpretation, and applications of risk ratio, rate ratio, odds ratio, and risk difference, highlighting their roles in different study designs. The distinction between probability and odds is clarified to prevent common misinterpretations, with examples illustrating their correct use. Mastery of these measures is essential for evaluating causal relationships, comparing risks across populations, and guiding public health decision-making.