  The advent of back-scattered laser beams for electron-positron colliders will
allow detailed studies of a large array of high energy photon-photon and
photon-electron collision processes with polarized beams. These include tests
of electroweak theory in photon-photon annihilation such as $\gamma \gamma \to
W^+ W^-$, $\gamma \gamma \to $ Higgs bosons, and higher-order loop processes,
such as $\gamma \gamma \to \gamma \gamma, Z \gamma, H^0 Z^0$ and $Z Z.$ Methods
for measuring the anomalous magnetic and quadrupole moments of the $W$ and $Z$
gauge bosons to high precision in polarized electron-photon and photon-photon
collisions are discussed. Since each photon can be resolved into a $W^+ W^-$
pair, high energy photon-photon collisions can also provide a remarkably
background-free laboratory for studying $W W$ collisions and annihilation. I
also review high energy $\gamma \gamma$ and $e \gamma$ tests of quantum
chromodynamics, including the production of two gluon jets in photon-photon
collisions, deeply virtual Compton scattering on a photon target, and
leading-twist single-spin asymmetries for a photon polarized normal to a
production plane. Exclusive hadron production processes in photon-photon
collisions provide important tests of QCD at the amplitude level, particularly
as measures of hadron distribution amplitudes which are also important for the
analysis of exclusive semi-leptonic and two-body hadronic B-decays.
