  For a set $\Omega$ an unordered relation on $\Omega$ is a family R of subsets
of $\Omega.$ If R is such a relation we let G(R) be the group of all
permutations on $\Omega$ that preserves R, that is g belongs to G(R) if and
only if x in R implies x^{g}\in R. We are interested in permutation groups
which can be represented as G=G(R) for a suitable unordered relation R on
$\Omega.$ When this is the case, we say that G is defined by the relation R, or
that G is a relation group. We prove that a primitive permutation group
different from the Alternating Group and of degree bigger or equal to 11 is a
relation groups. The same is true for many classes of finite imprimitive
groups, and we give general conditions on the size of blocks of imprmitivity,
and the groups induced on such blocks, which guarantee that the group is
defined by a relation. This property is closely connected to the orbit closure
of permutation groups. Since relation groups are orbit closed the results here
imply that many classes of imprimitive permutation groups are orbit closed.
