  We show that the N=2 open string describes a theory of self-dual Yang Mills
(SDYM) in (2,2) dimensions. The coupling to the closed sector is described by
SDYM in a Kahler background, with the Yang-Mills fields providing a source term
to the self-duality equation in the gravity sector. The four-point S-matrix
elements of the theory vanish, so the tree-level unitarity constraints leading
to the Chan-Paton construction are relaxed. By considering more general
group-theory ansatze the N=2 string can be written for any gauge group, and not
just the classical groups allowed for the bosonic and N=1 strings. Such ad hoc
group-theory factors can not be appended to the closed N=2 string, explaining
why the Z_n closed N=2 strings are trivial extensions of the Z_1 theory.
