Geometric methods in the algebraic theory of quadratic forms : Summer School Lens 2000 The geometric approach to the algebraic theory of quadratic forms is the study of projective quadrics over arbitrary fields. Function fields of quadrics have been central to the proofs of fundamental results since the 1960s. Recently more refined geometric tools have been brought to bear on this topic such as Chow groups and motives and have produced remarkable advances on a number of outstanding problems. Several aspects of these new methods are addressed in this volume which includes an introduction to motives of quadrics by A. Vishik with various applications notably to the splitting patterns of quadratic forms papers by O. Izhboldin and N. Karpenko on Chow groups of quadrics and their stable birational equivalence with application to the construction of fields withu invariant 9 and a contribution in French by B. Kahn which lays out a general framework for the computation of the unramified cohomology groups of quadrics and other cellular varieties. TOC:Cohomologie non ramifiée des quadriques (B. Kahn). Motives of Quadrics with Applications to the Theory of Quadratic Forms (A. Vishik). Motives and Chow Groups of Quadrics with Applications to the u invariant (N.A. Karpenko after O. T. Izhboldin). Virtual Pfister Neigbors and First Witt Index (O. T. Izhboldin). Some New Results Concerning Isotropy of Low dimensional Forms (O.T. Izhboldin). Izhboldins Results on Stably Birational Equivalence of Quadrics (N.A. Karpenko). My recollections about Oleg Izhboldin (A.S. Merkurjev)