Topological defects (aka topological solitons) appear in field theory models with spontaneous symmetry breaking and a non-trivial vacuum manifold. Cosmic strings are created whenever a U(1) symmetry gets spontaneously broken and are the topological defect that seems most important from the point of view of cosmological applications. There are several reasons for this: on the one hand it is believed that cosmic strings might be linked to the fundamental strings of String theory and on the other essentially all models that try to embed the Theory of Inflation into the scheme of Grand Unification predict the production of cosmic strings. Furthermore, the analysis of recent Cosmic Microwave Background (CMB) data suggests that cosmological models containing cosmic strings provide a better fit to both the temperature as well as polarization anisotropy data than inflaton and/or dust models alone. In the first part of my talk, I will discuss the “zoo” of cosmic strings available and also mention their gravitational properties. In the second part of my talk I will concentrate on superconducting strings. These are current-carrying strings, which can have an additional internal structure in the form of bosonic or fermionic fields. This internal structure can lead to the formation of vortons, i.e. loops of cosmic string that are balanced against collapse by a non-vanishing angular momentum.
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