It was brought out in Chapter 1 that the primary reason for sampling is to obtain estimates of population parameters that are of interest to a decision-maker. The decision-maker, naturally, would prefer knowledge of the parameters themselves but only rarely is it possible to obtain such knowledge at an acceptable cost in time or money. Consequently, the decision-maker usually must be satisfied with sample-based estimates of those parameters. In this chapter the estimation process will be explored and the foundation laid for later discussion of some of the sampling designs that may find application in land management operations.