Fritz Gesztesy and Konstantin A. Makarov Some Applications of the Spectral Shift Operator (91K, LaTeX) ABSTRACT. The recently introduced concept of a spectral shift operator is applied in several instances. Explicit applications include Krein's trace formula for pairs of self-adjoint operators, the Birman-Solomyak spectral averaging formula and its operator-valued extension, and an abstract approach to trace formulas based on perturbation theory and the theory of self-adjoint extensions of symmetric operators.