This is a comprehensive and timely text on multiphase flow and heat transfer for a nuclear engineer and those who are interested in nuclear reactor safety assessment, to have a picture of what may be happending in nuclear power plants under accident conditions, including hypothetical core meltdown situations. It is helpful since a majority of those who run reactor-safety computer codes do not have good grip on phenomenological understanding and models which formed the backbone of these codes. With respect to severe accidents, the author made a terrific attempt to go beyond the mundane of empiricism, but phenomena are too complex and there are too large uncertainties that somehow reduces the value of detailed modeling of particular processes. Knowledge gained to date in simulant-materials and small-scale experiments not necessarily provides the adequate picture of what could happen in reality.Especially since in most cases, measurements were indirect and models are speculative. Therefore a sense of caution is recommended to look behind equations and aware of where and how they were derived or conditions in which correlations were obtained.