This book is published in connection with the 100th anniversary of the Swedish National Forest Inventory, celebrated in 2023. It is an abbreviated version of the original Swedish publication. Initially, the prehistory, establishment, and development of the inventory are described. Based on collected data, the condition and changes of the Swedish forests over a century are then presented, as well as how data is collected, processed, and reported. Following that, some researchers describe how the inventory's data has been used in various disciplines. Collected data is also used by authorities, organizations, and businesses in their internal work, which is described by representatives. Predicting the future of the forests and their use is difficult, but in a concluding chapter, the likely future of the inventory is described and how it can be met to continue to provide answers in support of society's ambitions for sustainable forestry practices.