This volume contains papers based on talks delivered at the Third
Workshop on Quantum Field Theory under the /nftuence of External
Conditions held at the University of Leipzig from September 18th to
September 22nd, 1995. This series of Workshops is organized by the
quantum field theory group at the University of Leipzig. The first and
the second Workshop in the row have been held in 1989 and 1992. The
present meeting has been joined by more than 70 participants. This fact
underlines the vivid interest in the field covered by the Workshop
ranging from the Casimir effect to semiclassical gravity. The material
of this volume is organized along five subjects. The first part is
devoted to the Casimir effect itself. The actual interest is mostly in
non-stationary boundaries and a possible explanation of the phenomenon
of sonoluminescence - a still open and challenging question. The second
part deals with QED and QCD in external fields. The main interest was
focused on the effective action approach, on some aspects of the bag
model and on quantum effects in a conical background. The ground state
in external fields is studied in the contributions of the third part.
They demonstrate that the zeta function regularization tagether with the
heat kerne! expansion is the most powerful method at present. New
calculations of functional determinants, of finite temperature effects
and an interesting method applicable in the presence of smooth
background fields are presented.