This session will explain basic concepts associated with reserve variability and reserve ranges. It will start by describing the guidance that the Actuarial Standards of Practice are providing to practicing actuaries regarding the measurement of reserve uncertainty. Current market and regulatory trends that focus on the measurement of reserve uncertainty will also be described. In the second part of the session basic stochastic terminology will be explained in laymen terms. The audience should leave the session with a better understanding of the various types of risks measured in stochastic analysis and a basic understanding of the underlying ideas behind the most popular stochastic models and methods.