Where, when and how is our natural environment changing? What cause these changes? What will be the effects thereof? What might have to be done to mitigate and adapt to those changes? These questions are relevant to secure our environment for future generations. They must be answered by scientific observations over long time-scales, often at different localities or by meticulously designed experiments, either by using expensive instruments or by repeating the same observations over environmental gradients. The South African Environmental Observation Network (SAEON) is a national platform for detecting, translating and predicting environmental change through scientifically designed observation systems and research. SAEON captures and makes long-term datasets freely accessible to users, and runs an education-outreach programme. Structurally, SAEON comprises six distributed research nodes and a national office in Pretoria. Taken together, the six nodes represent the diverse landscapes, coastal areas, and the offshore marine environments in South Africa. Each node acts as an environmental observatory with its own field equipment and constellation of observation sites. SAEON focuses on in situ (ground-based and surface/underwater) observation, supplemented by the use of satellite imagery, other remote sensing observations and modelling. Mission statement: SAEON offers public value through long-term multi-disciplinary observation programmes and platforms that are designed to clarify Earth system dynamics and changes over multiple scales, and to distinguish between natural and anthropogenic environmental change. We develop open-access data systems and tools. We value excellence, data sharing, capacity development, stakeholder consultation, collaboration and a natural environment conducive to sustained life on Earth. SAEON is funded by the Department of Science and Technology and managed by the National Research Foundation of South Africa.