Preface; E. Folke Bolinder. Lecture Series Clifford Numbers and Spinors given by Professor Marcel Riesz, October 1957--January 1958. Preface. I. Clifford Numbers. II. Rotations and Reflections. III. Canonical Representations of Isometrics. IV. Representation of Isometrics by Infinitesimal Transformation and Clifford Bivectors. Bibliography. Index. Errata to Clifford Numbers and Spinors. Marcel Riesz's Lecture Notes on Clifford Algebra dictated to E. Folke Bolinder, April 1959. Marcel Riesz's Work on Clifford Algebras; P. Lounesto.