The early transition elements, especially vanadium, molybdenum and tungsten, form a vast number of polyoxoanions with remarkable structures, unprecedented combinations of properties and relevance to disciplines ranging from mathematics to medicine. Although the first examples of these substances were described in the mid-19th century, it is only within the last 20-30 years that the field has begun to receive the attention it deserves. This book contains 28 review chapters by leading investigators who participated in an international workshop held in Bielefeld in July 1992. It provides a survey of recent and current activity in this field - including new synthetic methods and new structural types; topological analysis of polyhedral structures; discrete polyoxoanions as models for metal oxide lattices, magnetic interactions and domains; donor-acceptor and host-guest chemistry; organic and organometallic derivatives; mixed valence and electron transfer; homogeneous and heterogeneous redox and acid catalysis; photochemistry and photocatalysis; polyoxoanion-protein chemistry; antitumour and anti-HIV activity.