  This paper provides a construction of the unipotent representations for
classical complex groups in terms of the Theta correspondence as introduced and
studied by R. Howe. The K-type structure of unipotent representations is
obtained as a consequence of the character formulas for unipotent
representations of D. Vogan and the author. This provides a tight link between
unipotent representations and the orbit philosophy. A parametrization of
unipotent representations for the Spin groups is obtained.
