Sampling Theory is a branch of statistics that focuses on the selection of individual observations from a larger population to estimate characteristics of that population. It provides the foundation for making inferences about a population based on a sample, which is a smaller, manageable subset of the population. The theory encompasses various sampling methods, such as random sampling, stratified sampling, and systematic sampling, each with its own advantages and applications. By understanding Sampling Theory, researchers can design studies that yield reliable and valid results, ensuring that their findings are representative of the broader population.