This chapter provides a brief summary of the relevant concepts of probability and random variables. It also introduces some concepts of estimation that are essential for signal analysis. Many situations occur that involve nondeterministic or random phenomena. Similarly there are many signal and time series measurements with random characteristics. Their behavior is not predictable with certainty because of several reasons. To analyze and understand these phenomena, a probabilistic approach must be used. The concepts and theory of probability and estimation provide a fundamental mathematical framework for the techniques of analyzing random signals. It begins by exploring random variables and their various properties. The concept of joint probability is also described here, which is very important in signal analysis. The joint probability density function and its moments are the basis for describing any interrelationships or dependencies between the two variables. It also discusses numerous general properties of estimators including convergence, recursion, and maximum likelihood estimation. The last section describes random numbers and signal characteristics. Signals with known characteristics are often needed to test signal processing procedures or to simulate signals with specific properties. This section introduces methods to generate random signals with different first order probability characteristics.