This concise introductory treatment consists of three chapters: The Geometry of Hilbert Space, The Algebra of Operators, and The Analysis of Spectral Measures. A background in measure theory is the sole prerequisite. "An exposition which is always fresh, proofs which are sophisticated, and a choice of subject matter which is certainly timely." - Bulletin of the American Mathematical Society. AUTHOR: Hungarian-born Paul R. Halmos (1916 2006) is widely regarded as a top-notch expositor of mathematics. He taught at the University of Chicago and the University of Michigan as well as other universities and made significant contributions to several areas of mathematics, including mathematical logic, probability theory, ergodic theory, and functional analysis.