Subfactors have been a subject of considerable research activity for about fifteen years and are known to have significant relations with other fields such as low dimensional topology and algebraic quantum field theory. These notes give an introduction to the subject suitable for a student who has only a little familiarity with the theory of Hilbert space. A new pictorial approach to subfactors is presented in a late chapter.

‘The presentation is a pleasure to read, and the careful selection of topics leads the reader on a very direct route to some of the most fascinating problems and results in the theory of von Neumann algebras … an excellent introduction at graduate level to current research in this field.’

Source: Monatshefte für Mathematik

‘This book is a model of clear exposition and keen pricing. Those working in operator algebras will find it self-recommending, and research students and others outside the area wishing to learn the subject need look no further. It is a most valuable addition to the literature.’

Bull. London Math. Soc.

‘The book is compact and well written …’

Source: European Mathematical Society