Circular Strings in De Sitter Spacetime

String propagation is investigated in de Sitter and black hole backgrounds using both exact and approximative methods. The circular string evolution in de Sitter space is discussed in detail with respect to energy and pressure, mathematical solution and physical interpretation, multi-string solutions etc. We compare with the circular string evolution in the 2+1 dimensional black hole anti de Sitter spacetime and in the equatorial plane of ordinary 3+1 dimensional stationary axially symmetric spacetime solutions of Einstein general relativity. Using an approximative string perturbation approach we consider also generic string evolution and propagation in all these curved spacetimes. (To appear in the proceedings of the 2eme Journee Cosmologie held in Paris, June 1994)