By gluing together the sides of eight copies of an all-right angled hyperbolic 6-dimensional polytope, two orientable hyperbolic 6-manifolds with Euler characteristic −1 are constructed. They are the first known examples of orientable hyperbolic 6-manifolds having the smallest possible volume.The n-dimensional manifold Siegel problem. Determine the minimum possible volume obtained by an orientable hyperbolic n-manifold.All hyperbolic manifolds in this paper will be complete Riemannian manifolds of constant sectional curvature −1. The "full" Siegel problem refers to the problem above for orbifolds rather than manifolds. Nevertheless, the manifold Siegel problem is one with a long and venerable history. This paper describes our solution when n = 6. But first, an overview and some background. The Euler characteristic χ creates a big difference between even and odd dimensions. When n is even, the Gauss-Bonnet theorem gives vol(M ) = κ n χ(M ), with κ n = (−2π) n 2 /(n − 1)!! for the volume of an n-dimensional hyperbolic manifold M . As χ(M ) ∈ Z, the most obvious place to look for solutions to the problem is when |χ| = 1. A compact orientable M satisfies |χ(M )| ∈ 2Z, so the minimum volume is most likely achieved by a non-compact manifold. When n is odd, χ(M ) = 0, and a different approach must be found. For these reasons progress in even dimensions has been more rapid.