  We summarize results on the reliability of the eikonal approximation in
obtaining the high energy behavior of a two particle forward scattering
amplitude. Reliability depends on the spin of the exchanged field. For scalar
fields the eikonal fails at eighth order in perturbation theory, when it misses
the leading behavior of the exchange-type diagrams. In a vector theory the
eikonal gets the exchange diagrams correctly, but fails by ignoring certain
non-exchange graphs which dominate the asymptotic behavior of the full
amplitude. For spin--2 tensor fields the eikonal captures the leading behavior
of each order in perturbation theory, but the sum of eikonal terms is
subdominant to graphs neglected by the approximation. We also comment on the
eikonal for Yang-Mills vector exchange, where the additional complexities of
the non-abelian theory may be absorbed into Regge-type modifications of the
gauge boson propagators.
