The genius of Carl Friedrich Gauss (1777-1855) and the novelty of his work (published in Latin, German, and occasionally French) in areas as diverse as number theory, probability and astronomy were already widely acknowledged during his lifetime. But it took another three generations of mathematicians to reveal the true extent of his output as they studied Gauss' extensive unpublished papers and his voluminous correspondence. This posthumous twelve-volume collection of Gauss' complete works, published between 1863 and 1933, marks the culmination of their efforts and provides a fascinating account of one of the great scientific minds of the nineteenth century. Volume 8, published in 1900, supplements the first four volumes with further work on number theory, probability and differential geometry that was discovered posthumously among Gauss' papers. Gauss here engages with work by scholars including Lagrange, Legendre, Lobatschewsky and Moebius, and paves the way for non-Euclidean geometry.