This book reflects our own struggle to understand the semiclassical
behaviour of quantized fields in the presence of boundaries. Along many
years, motivated by the problems of quantum cosmology and quantum field
theory, we have studied in detail the one-loop properties of massless
spin-l/2 fields, Euclidean Maxwell the- ory, gravitino potentials and
Euclidean quantum gravity. Hence our book begins with a review of the
physical and mathematical motivations for studying physical theories in
the presence of boundaries, with emphasis on electrostatics, vacuum v
Maxwell theory and quantum cosmology. We then study the Feynman
propagator in Minkowski space-time and in curved space-time. In the
latter case, the corre- sponding Schwinger-DeWitt asymptotic expansion
is given. The following chapters are devoted to the standard theory of
the effective action and the geometric im- provement due to Vilkovisky,
the manifestly covariant quantization of gauge fields, zeta-function
regularization in mathematics and in quantum field theory, and the
problem of boundary conditions in one-loop quantum theory. For this
purpose, we study in detail Dirichlet, Neumann and Robin boundary
conditions for scalar fields, local and non-local boundary conditions
for massless spin-l/2 fields, mixed boundary conditions for gauge fields
and gravitation. This is the content of Part I. Part II presents our
investigations of Euclidean Maxwell theory, simple super- gravity and
Euclidean quantum gravity.