Bulk metallic glass (BMGs) forming alloys are fascinating, which possess a wide spectrum of scientifically interesting and technologically applicable properties. Their structures remain an unsolved puzzle and the composition design criteria are desirable. They are currently among the most actively studied metallic materials. In this book, we introduce the structure models and formation criteria of metallic glasses and a structure formation theory. Phase transformations of Zr-based alloys are studied. We ask in the early stage structure formation how the valence electrons and the static structure resonantly couple to each other to depress effectively the total energy. We generalize the atomic cluster concept and propose a spatial averaged structure picture of BMG. A BMG composition design strategy is finally presented and their electrical transport properties are studied. This book takes the subject matter of current research interest. It is intended that this book should stimulate new research interests in the metallic glass field. It is also hoped that this book will be found useful to research students of materials science.