Satellite validation has to ensure that geophysical quantities derived from in-orbit radiometric measurements meet quality requirements for the intended scientific studies and applications. It is not a 'once a mission lifetime' task, but requires regular proof measurements throughout the in-orbit phase. An extensive SCIAMACHY validation programme has been developed jointly by Germany, The Netherlands and Belgium, with the support of ESA and a large number of international partners. Due to its status as an AO instrument SCIAMACHY is embedded in two collaborating validation structures, ESA's Atmospheric Chemistry Validation Team and the SCIAVALIG, a subgroup of the SCIAMACHY Science Advisory Group. In the first years of the mission intensive independent measurement campaigns were organised, setting the basis for a continuous validation programme over the instrument lifetime, harmonised with the steadily improving operational processors and the scientific algorithms. All validation activities have to obey well-established validation principles including a thorough analysis when comparing geophysical parameters derived from SCIAMACHY with correlative measurements. Such measurements use all available means-from ground, ships, aircraft and balloons. Additionally the SCIAMACHY measurements were compared with results from other space-borne atmospheric sensors. Meanwhile validation has confirmed the current accuracy for a wealth of retrieved parameters. The list includes O3, NO2, BrO, OClO, SO 2, HCHO, CHOCHO, H2O, CO, CO2, CH4, cloud fraction and cloud top pressure, aerosol index and aerosol optical thickness.