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...