Stochastic hydrogeology, which emerged as a research area in the late 1970s, involves the study of subsurface, geological variability on flow and transport processes and the interpretation of observations using existing theories. Lacking, however, has been a rational framework for modeling the impact of the processes that take place in heterogeneous media and for incorporating it in predictions and decision-making. This book provides this important framework. It covers the fundamental and practical aspects of stochastic hydrogeology, coupling theoretical aspects with examples, case studies, and guidelines for applications.