This book studies properties of pseudo-differential operators arising in quantum mechanics as bounded linear operators on $ L ن2ü(BbbR نnü) $. The results and methods should be of interest to graduate students and mathematicians working in Fourier analysis, operator theory, pseudo-differential operators and mathematical physics. Background materials are given in adequate detail to enable a graduate student to proceed rapidly from the very basics to the frontier of resarch in an area of operator theory.