This book documents the recent focus on a branch of Riemannian geometry called Comparison Geometry. The simple idea of comparing the geometry of an arbitrary Riemannian manifold with the geometries of constant curvature spaces has seen a tremendous evolution recently. This volume is an up-to-date reflection of the recent development regarding spaces with lower (or two-sided) curvature bounds. The content reflects some of the most exciting activities in comparison geometry during the year and especially of the Mathematical Sciences Research Institute's workshop devoted to the subject. This volume features both survey and research articles. It also provides complete proofs: in one case, a new, unified strategy is presented and new proofs are offered. This volume will be a valuable source for advanced researchers and those who wish to learn about and contribute to this beautiful subject.

1. Scalar curvature and geometrization conjectures for 3-manifolds Michael T. Anderson; 2. Injectivity radius estimates and sphere theorems Uwe Abresch and Wolfgang T. Meyer; 3. Aspects of Ricci curvature Tobias H. Colding; 4. A genealogy of noncompact manifolds of nonnegative curvature: history and logic R. E. Greene; 5. Differential geometric aspects of Alexandrov spaces Yukio Otsu; 6. Convergence theorems in Riemannian geometry Peter Petersen; 7. The comparison geometry of Ricci curvature Shunhui Zhu; 8. Construction of manifolds of positive Ricci curvature with big volume and large Betti numbers G. Perelman; 9. Collapsing with no proper extremal subsets G. Perelman; 10. Example of a complete Riemannian manifold of positive Ricci curvature with Euclidean volume growth and with nonunique asymptotic cone G. Perelman; 11. Applications of quasigeodesics and gradient curves Anton Petrunin.