A survey of K-theory -- Characterizing Ext(X) -- Almost commuting algebras -- Extensions of C*-algebras and K-homology -- Bundles and sheaves are equivalent in the category of banach spaces -- Topological obstructions to perturbations of pairs of operators -- On algebraic K-theory and the homology of congruence subgroups -- Configuration spaces -- Extensions of C*-algebras and the reducing essential matricial spectra of an operator -- K-homology theory and algebraic K-theory -- Some remarks on operator theory and index theory -- Factors of type III -- Twisted products of Banach algebras and third ?ech cohomology -- H-cobordisms, pseudo-isotopies, and analytic torsion