Magnetic and electric field effects in semiconductor quantum microcavity structures T. A. Fisher, A. M. Afshar, D. M. Whittaker, Maurice S. Skolnick, P. Kinsler, J. S. Roberts, G. Hill, M. A. Pate, Department of Physics/Department of Electronic and Electrical Engineering University of Sheffield, Sheffield S3 7RH, United Kingdom. NATO ASI E324, 77 (1996). "Microcavities and photonic bandgaps: Physics and Applications", Eds. J. Rarity, C. Weisbuch. DOI: 10.1007/978-94-009-0313-5_7 The effects of magnetic and electric field on the vacuum Rabi exciton-photon coupling in semiconductor quantum microcavity structures are presented. A number of phenomena are described including marked increase (decrease) of the vacuum Rabi coupling in external magnetic (electric) field due to the increased (decreased) exciton oscillator strength, exciton Zeeman splitting, and unusual linewidth narrowing effects attributed to motional narrowing.