The Ninth Course of the International School of Cosmology and Gravita-
tion of the Ettore Majorana Centre for Scientific Culture is concerned
with "Topological Properties and Global Structure of Space-Time." We
consider this topic to possess great importance. Our choice has also
been influenced by the fact that there are many quest ions as yet unre-
solved. Standard general relativity describes space-time as a
four-dimensional pseudo-Riemannian manifold, but it does not prescribe
its large-scale structure. Inorderto attempt answers to some topological
questions, such as whether our universe is open or closed, whether it is
orientable, and whether it is complete or possesses singularities,
various theoretical approaches to global aspects of gravitational
physics are presented here. As topological questions playa role in
non-standard theories as weIl, it will be found that some of the
lectures and seminar talks in this volume adopt the point of view of
standard relativity, whereas others are based on different theories,
such as Kaluza-Klein theories, bimetric theories, and supergravity. We
have found it difficult to organize these papers into classes, say
standard and non-standard theory, or models with and without
singularities. One paper, by R. Reasenberg, is experimental. Its purpose
was to give the theorists present an inkling of the opportunities, as
weIl as the pitfalls, of experimental research in gravitational physics.
Accordingly, we have arranged all contributions alphabetically, by
first-named) author.