More than a century after Faraday, there remains in the field of motors and drives enormous scope for innovation. This presentation of the theory of brushless d.c. drives will help engineers to appreciate the potential of such motors and apply them more widely, taking advantage of remarkable and recent developments in permanent-magnet materials, power semiconductors, electronic control, and motor design (including CAD). The objective is not to "sell" particular technologies or to teach design, but to lay out the basic principles and to raise the general credibility and acceptance of new technology that many engineers have striven to establish. The sections on the permanent magnets and magnetic circuits will assist in the exploitation of new PM materials with outstanding properties. Although the approach is essentially academic (theory and calculation predominates), the text is augmented with examples and practical applications of interest to practicing electronics engineers.