This section provides an introduction to environmental statistics and data and covers the state of existing data and knowledge that contribute to any environmental assessment, including national-, regional- and global-level assessments. It attempts to elaborate the state of data collection and the use of data to compile statistics and produce indicators. Emerging areas of statistics, such as big data, citizen science and traditional knowledge – which are currently underutilized, but present tremendous opportunities for better measuring – are discussed in Chapter 25 of this report.