Topological Defects in Cosmology

Topological Defects like magnetic monopoles, cosmic strings, domain walls, etc., could have formed during symmetry breaking phase transitions in the early universe. We give an overview of the implications of topological defects for cosmology, with particular emphasis on their possible role as sources of the extremely high energy cosmic rays detected in several recent cosmic ray experiments; these experiments may indeed provide the signature of existence of topological defects in the Universe. : : : still I cannot close without stating the simple fact that I and everyone of my colleagues who share the title of astrophysicist is personally in your debt. It is a very happy event to see a portion of that debt recognized in this fashion. Please accept my warmest congratulations. It is hard to imagine a Nobel Award that would be as widely and enthusiastically approved by physicists and astronomers.