An affine transformation T on a
group G is an automorphism followed by a translation; T is transitive if for each
x,y ∈ G there is an integer n such that Tn(x) = y. All groups with transitive
affine transformations are determined: the infinite cyclic and infinite dihedral
group are the only infinite examples; while the finite examples are semi-direct
products of certain odd-order groups by a cyclic, dihedral or quaternion
2-group. The automorphism groups of the above groups are described, and the
automorphisms which occur as parts of transitive affine transformations are
given.