Theodosius' 'Sphaerica', on the geometry of the sphere, was one of many Greek mathematical works translated into Arabic in ninth-century Baghdad. It was also one of the mathematical works translated from Arabic into Latin in the twelfth century as part of the 'Little Renaissance' in the West. In this book one Arabic translation is edited, accompanied by Gerard of Cremona's Latin translation. The edition is followed by a mathematical summary for modern readers. This parallel Arabic-Latin edition can be regarded as a model for the treatment of scientific texts from classical antiquity that have reached us through a series of translations.