This documentation has been prepared by ESA and the Euclid Consortium. The preparation was lead by Hervé Aussel (CNRS, AIM) and Xavier Dupac (ESA-ESAC). Initial development of the file by John Hoar (ESA-ESAC). The authors acknowledge the work of the Gaia DPAC work package 920 ‘Documentation’, whose high quality work provided both the technical and structural foundation for this document. The HTML version of this documentation has been produced with the LaTeX to XML/HTML/MathML converter LaTeXML developed by Bruce Miller at the US National Institute of Standards and Technology (NIST). The names of contributors of chapters and (sub)sections are provided in the documentation.