This volume contains the proceedings of the International Workshop on Operator Theory and Applications (IWOTA 2006) held at Seoul National University, Seoul, Korea, from July 31 to August 3, 2006. The special interest areas of this workshop were Hilbert/Krein space operator theory, complex function theory related to Hilbert space operators, and systems theory related to Hilbert space operators. This volume contains sixteen research papers which reflect recent developments in operator theory and applications.<BR>This book is written for postgraduates and researchers in operator theory, complex function theory, systems theory and applications.