  Using the strong electromagnetic fields in peripheral heavy ion collisions
gives rise to a number of interesting possibilities of applications in both
photon-photon and photon-hadron physics. We look at the theoretical foundations
of the equivalent photon approximation and the specific problems in the heavy
ion case. The interesting physics processes that can be studied in this way are
outlined. Electron positron pair production plays a special role. We look at
multiple pair production and Coulomb corrections as typical strong field
effects. But electron positron pair production is also an important loss
process and has some practical applications.
