This 2005 book is targeted to graduate students and researchers at the cutting edge of investigations into the fundamental nature of multiphase flows. It is intended as a reference book for the basic methods used in the treatment of multiphase flows. The subject of multiphase flows encompasses a vast field, a host of different technological contexts, a wide spectrum of different scales, a broad range of engineering disciplines, and a multitude of different analytical approaches. The aim of Fundamentals of Multiphase Flow is to bring much of this fundamental understanding together into one book, presenting a unifying approach to the fundamental ideas of multiphase flows. The book summarizes those fundamental concepts with relevance to a broad spectrum of multiphase flows. It does not pretend to present a comprehensive review of the details of any one multiphase flow or technological context; references to such reviews are included where appropriate.