This volume is dedicated to Bill Helton on the occasion of his sixty fifth birthday. It contains biographical material, a list of Bill's publications, a detailed survey of Bill's contributions to operator theory, optimization and control and 19 technical articles. Most of the technical articles are expository and should serve as useful introductions to many of the areas which Bill's highly original contributions have helped to shape over the last forty odd years. These include interpolation, Szegö limit theorems, Nehari problems, trace formulas, systems and control theory, convexity, matrix completion problems, linear matrix inequalities and optimization.The book should be useful to graduate students in mathematics and engineering, as well as to faculty and individuals seeking entry level introductions and references to the indicated topics. It can also serve as a supplementary text to numerous courses in pure and applied  mathematics and engineering, as well as a source book for seminars.

Original articles present a broad range of cutting-edge research

Preface.- Inroduction (an overview of the contents of the book, from the perspective of Helton's landmark contributions).- Biographical Note and List of Publications of J.W. Helton.- Bounded Analytic Interpolation and H-infinity Control.- Linear Matrix Inequalities and Matrix Convexity.- Optimization and Realization in the Free *-algebra.- Automatic Verification of Matrix Inequalities.- Non-commutative Algebraic Geometry.- Non-Commutative Differential Geometry and Probability.- Modern Trends in Robust Control.- Challenges of Mathematical Biology.- Mathematical Programming and Computer Science.