Cryogenic systems that involve two-phase (vapor-liquid) flows are widely used in aerospace, metallurgy, power engineering, and high energy physics research. This book describes characteristic features of cryogenic systems involving two-phase flow, creates mathematical models of these systems, and shows how the models may be used to develop optimal designs for practical cryogenic systems. The authors pay particular attention to the important topic of transient phenomena in cryogenic systems. Many examples are based on large Russian systems in space technology, energy research, and particle physics.