This volume examines a timely problem in solid state physics, the condensation of ex­ citons in semiconductors. The papers in this volume describe a new approach to the study of exciton condensation based on microwave-frequency conductivity and the breakdown of an ex­ citon gas in a microwave field, an effect discovered by the authors. These methods have been used in extensive studies of germanium and have produced important new data about the con­ densation process. In addition to the experimental data, a theory is presented for the micro­ wave breakdown of excitons in the presence of electron-hole droplets. Also included are three articles devoted to the experimental aspects of low-temperature semiconductor research. This volume will interest scientists and engineers involved· with research in solid state physics. CONTENTS Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 A. A. Manenkov Microwave Studies of Exciton Condensation in Ge. . . . . . . . . . . . . . . . . . . . . . . . . . 3 G. N. Mikhailova Microwave Breakdown of Excitons and the Kinetics of Free Carriers and Excitons in Germanium in the Presence of Electron-Hole Drops. . . . . . . . . . . . . 37 A. A. Manenkov, V. A. Milyaev, G. N. Mikhailova, V. A. Sanina, and A. S.