The topic of this chapter is the statistical sampling approach of the Swiss National Forest Inventory (NFI). We start with the main populations and population parameters of interest, and how these are – under the infinite population or Monte-Carlo approach to forest inventory – re-shaped into and understood as continuous populations in space. The spatial arrangement of field data collection on a grid of permanently installed sample plots recently changed from a periodic into a continuous (annual) system, which are presented in the following sections, together with estimation procedures which make use of remote sensing and other spatial data to increase the precision of the estimates. We then emphasise on the estimation of change and change components, and depict specific solutions such as for the estimation of the average annual change and the change per unit area. Finally, the NFI system of two-stage subsampling of tally trees for stem volume estimation and the respective estimation procedures are described in this chapter.