This volume contains the proceedings of the international conference on " Operator Calculus and Spectral Theory" in Lambrecht, Germany, Decem- ber 9. - 14. , 1991, sponsored by the Deutsche Forschungsgemeinschaft, and by the Karl-Weierstrass-Institute of Mathematics, Berlin. The idea was to bring together specialists from different areas of modern analysis, geometry and mathematical physics, in a similar spirit as in the earlier series of conferences of the Karl-Weierstrass- Institute (Ludwigsfelde, 1976; Reinhardsbrunn, 1985; Holzhau, 1988; Breitenbrunn,1990). Berlin, Mainz M. Demuth B. Gramsch B. -W. Schulze List of talks given in La. brecht. 8. - 14. December 91 Name Title S. Albeverio Some recent deveiopments in Dirichlet forms and associated processes U. Bunke On the spectral flow of Dirac operators with negative definite functions as symbols - applications in probability theory and mathematical physics M. Combescure Recurrent versus diffusive behaviour for time-dependent quantum Hamiltonian E. B. Davies Analysis on graphs and noncommutative geometry M. Demuth On stochastic spectral analysis and asymptotics for Schrodinger operators P. Duclos A global approach to the location of quantum resonances v. v. Egorov On negative spectrum of elliptic operators V. EnB Non-threshold states of long-range N-body problems B. Gramsch -algebras and microlocal analysis P. B. Gilkey On the index of geometrical operators for Riemannian manifolds with boundary B. Helffer Spectral problems in statistical mechanics R. Hempe I Second order pertubations of elliptic operators with periodic principal part T. Ichinose On the Weyl quantized relativistic Hamiltonian V. V.