Open Strings in Constant Electric and Magnetic Fields

Various properties of open strings in external constant E.M. fields are reviewed. In particular, the charged-particle pair production rate in an external electric field is evaluated, and shown to reduce to Schwinger's formula in the limit of low-intensity fields. Open strings in external magnetic fields are shown to undergo an infinite number of phase transitions as the strenght of the field increases. (Talk given at the conference ``Strings '93'', Berkeley, CA, (May 24-29, 1993) to appear in the proceedings.)