This book presents novel observational evidence toward detecting and characterizing the products of massive, interacting binary stars. As a majority of massive stars are born in close binary systems, a large number of so-called massive binary interaction products are predicted to exist; however, few have been identified so far. Based on observations with the largest telescopes around the world, equipped with state-of-the-art instrumentation, this book helps to remedy this situation. In her outstanding PhD-thesis Julia Bodensteiner identifies a new class of post-interaction binaries in a...