The Swiss National Forest Inventory (NFI) is a forest survey on national level which started in 1982 and has already reached its 5th survey cycle (NFI5). It can be characterized as a multisource and multipurpose inventory where information is mainly collected from terrestrial field surveys using permanent sample plots. In addition, data from aerial photography, GIS and forest service questionnaires are also included. The NFI's main objective is to provide statistically reliable and sound figures to stakeholders such as politicians, researchers, ecologists, forest service, timber industry, national and international organizations as well as to international projects such as the Forest Resources Assessment of the United Nations. For Switzerland, NFI results are typically reported on national and regional level. State of the art methods are applied in all fields of data collection which have been proven to be of international interest and have even served as a basis for other European NFIs. The presented methods are applicable to any sample based forest inventory around the globe. In 2001 the Swiss NFI published its methods for the first time. Since then, many methodological changes and improvements have been introduced. This book describes the complete set of methods and revisions since NFI2. It covers various topics ranging from inventory design and statistics to remote sensing, field survey methods and modelling. It also describes data quality concepts and the software framework used for data storage, statistical analysis and result presentation.