In mathematics, the Hessian group is a finite group of order 216, introduced by Jordan (1877) who named it for Otto Hesse, given by the group of determinant 1 affine transformations of the affine plane over the field of 3 elements. It acts on the Hesse pencil and the Hesse configuration. Its triple cover is a complex reflection group of order 648, and the product of this with a group of order 2 is another complex reflection group.