This book intended to cover the overview of unequal probability sampling and Generalization of Murthy''s (1957) estimator. The researcher in the field of survey sampling can get benefit from this book. This book covers an overview of the unequal probability sampling, work done for Horvitz and Thompson (1952), Raj(1956) and Murthy (1957) estimators. Simulation and Empirical studies are conducted to discuss the performance of various available estimators for unequal probability sampling.