The field assessment is the most important source of data for the Swiss National Forest Inventory (NFI). In NFI4 the regular terrestrial survey contained 7455 sample plots, of which 6357 were accessible and classified as ‘forest’ or ‘shrub forest’. On each forest or shrub-forest sample plot, around 280 different attributes were assessed. The individual work steps for assessing a sample plot as well as the equipment and tools used, are explained in detail.