Dynamo theory is the study of how large-scale magnetic fields can arise in bodies such as the Earth, Sun and stars, and it brings together researchers in such diverse subjects as geophysics, astronomy and nuclear reactor technology. In this book are papers on the theory of dynamos, delivered at the Isaac Newton Institute for Mathematical Sciences in Cambridge in September 1992, and these have been carefully brought together to form a unified presentation. Topics covered include: modelling of solar magnetic field generation, theoretical studies of the galaxies, and papers on 'fast dynamos', study of magnetic field regeneration in fluid of very high electrical conductivity. This volume represents a comprehensive record of research into the theory of dynamos.