Studies on queuing models and their publication in professional journals and textbooks have been sparse over the past eleven decades. Collections of some of these studies have appeared either as single volumes or just chapters of single volumes and/or monographs. This book is an attempt to present some queuing models, especially those applicable in business and industry, in a style between a monograph and a textbook. Also the need of researchers and practitioners for a handbook-type text and the current lack of it explain the need for a book of this kind. Most of the basic terminologies and concepts that appear throughout the text are introduced in a systematic way in the first two chapters; nevertheless, previous exposition to a first course in probability and statistics is advised for later chapters. The principal audiences for the book are senior undergraduates (first three chapters) and graduate students (all six chapters). It is also a hope that the volume will appeal to a wider audience of specialists and researchers in mathematical science, engineering, physics, business and economics.