Main steps of the EDR3 astrometry processing and their place in the cyclic processing scheme of DPAC. Gaia EDR3 (and DR3) are generated in the third processing cycle (cycle 3). The stretches of observational data processed in the different cycles are indicated by thick horizontal lines. The boxes connected by arrows show the sequence of processing steps and their interdependencies, but they are not placed chronologically on the timeline. Only steps directly relevant for the astrometry are shown, leaving out most of the complexities of the full DPAC processing. No details are given for DR1. The first month of the nominal mission, with observations made in the ecliptic pole scanning law (EPSL) mode, was not used for the astrometry in DR2 and EDR3, but may be incorporated in later releases. The Whitehead eclipse avoidance manoeuvre (WEAM) on 16 July 2019 marks the beginning of the extended mission. In the first year of the extended mission (data segments DS6 and DS7), scanning was made in the reversed precession mode (Sect. 6.4). The processes SDM, CALIPD, AGIS, and PhotPipe are explained in Sect. 2.1.