When visiting M.I.T. for two weeks in October 1994, Victor Guillemin
made me enthusiastic about a problem in symplectic geometry which
involved the use of the so-called spin-c Dirac operator. Back in
Berkeley, where I had l spent a sabbatical semester, I tried to
understand the basic facts about this operator: its definition, the main
theorems about it, and their proofs. This book is an outgrowth of the
notes in which I worked this out. For me this was a great learning
experience because of the many beautiful mathematical structures which
are involved. I thank the Editorial Board of Birkhauser, especially Haim
Brezis, for sug- gesting the publication of these notes as a book. I am
also very grateful for the suggestions by the referees, which have led
to substantial improvements in the presentation. Finally I would like to
express special thanks to Ann Kostant for her help and her prodding me,
in her charming way, into the right direction. J.J. Duistermaat Utrecht,
October 16, 1995.