Two permutation groups G, H ≤ Sym(Ω) are called orbit equivalent if they have the same orbits on the power set of
Ω. Primitive orbit equivalent permutation groups were
determined by Seress. In this thesis we prove results toward the
classification of two-step imprimitive, orbit equivalent
permutation groups, which is the next natural step in the program
of classifying all transitive, orbit equivalent pairs.
Along the way, we also prove that with a short explicit list
of exceptions, all primitive groups have at least four regular
orbits on the power set of the underlying set.