This book is a collection of the invited lectures given at the International Workshop on "Electron Magnetic Resonance of Disordered Systems" (EMARDIS) held in Pravetz, Bulgaria from 7 to 10 July 1989. Its aim was to cover all aspects of recent development in the theory, methodology, experiment, instrumentation, etc. of Electron Magnetic Resonance (EPR, ENDOR, ESE) spectroscopy of disordered systems.