Mathematical Preliminaries.- Conformal Transformations and Conformal Killing Fields.- The Conformal Group.- Central Extensions of Groups.- Central Extensions of Lie Algebras and Bargmann's Theorem.- The Virasoro Algebra.- First Steps Towards Conformal Field Theory.- Representation Theory of the Virasoro Algebra.- Projective Representations of Diff+ ( ) and More.- String Theory as a Conformal Field Theory.- Foundations of Two-Dimensional Conformal Quantum Field Theory.- Mathematical Aspects of the Verlinde Formula.