The eighteenth International Workshop on Operator Theory and Applications (IWOTA) was hosted by the Unit for Business Mathematics and Informatics of the North-West University, Potchefstroom, South Africa from July 3 to 6, 2007. The conference was dedicated to Professor Joseph A. Ball on the occasion of his 60th birthday and to Professor Marinus M. Kaashoek on the occasion of his 70th birthday, and we wish to similarly honour them by dedicating this volume of the proceedings to them. TheaimoftheIWOTAmeetingsistobringtogethermathematiciansworking in operator theory and its applications to related ?elds. Each conference therefore has a unique character, depending on the related ?elds chosen by the local or- nizers. In the present case Functional Analysis and Von Neumann algebras were decided on, due to the number of people actively working in those ?elds in South Africa. The meetings are intended to be truly international (the seventeen pre- ous ones were held in 11 di?erent countries) and this conference was no exception, with participants drawn from 17 countries. IWOTA is directed by an international steering committee of 25 members under the guidance of the president I. Gohberg (Tel Aviv), assisted by the Vice PresidentsJ.W.Helton(LaJolla)andM.A.Kaashoek(Amsterdam).TheProce- ings of the IWOTA workshops regularly appear in the Birkhauser .. series: Operator Theory: Advances and Applications, and we thank them for their willingness to continue this cooperation by publishing this volume.