  This article is based on a talk given at the IInd International Colloquium on
Modern Quantum Field Theory, Bombay 1994. The Ernst solution of dilaton gravity
describes charged black holes undergoing uniform accleration in a background
magnetic field. By analytically continuing the Ernst solution one obtains
instantons that describe the pair production of black holes in the background
field. We review various aspects of these solutions paying special attention to
the Einstein-Maxwell, low-energy string and $d=5$ Kaluza-Klein theories. It is
based on work done in collaboration with {}F. Dowker, S. Giddings, G. Horowitz,
D. Kastor and J. Traschen \refs{\DGKT,\DGGH}.
