In this chapter, we present the basic principles of statistical estimation as they relate to the other parts of this book. Statistical estimation theory has a wide range of applications in solving real-world problems, some of which are presented in this book. For example, determining the location of a moving object can be formulated as an estimation problem. Estimation of the frequency of sinusoidal signals is also a common practical problem, such as estimating the speed of a vehicle. Designing precoders and equalizers in the transceivers of multi-input multi-output (MIMO) communication systems also calls for estimation methods.