This book surveys the current status of the field. It begins with an overview of the physics and chemistry of organic light emitting devices by J. Shinar and V. Savvateev. It then turns to the design of molecular materials for high performance devices (C. Adachi and T. Tsutsui) and a discussion of chemical degradation and physical aging (K. Higginson, D.L. Thomsen, B. Yang, and F. Papadimitrakopoulos). A. Dodabalanpur describes microcavity LEDs, and Y. Shi, J. Liu, and Y. Yang discuss polymer morphology and device performance. Various aspects of devices based on polyparaphenylenes are discussed in chapters by N.C. Greenham and R.H. Friend; by Chayet, Savvateeyv, Davidoff and Neumann; and by S. Tasch, W. Graupner, and G. Leising. The book concludes with a discussion of devices based on pyridine-containing conjugated polymers by Y.Z. Wang, D. Gebler, and A.J. Epstein