It has been almost thirty years since the publication of the classic book with a similar title, written by Clift, Grace and Weber. During this time a vast body of literature on particles, bubbles and drops have been created. The field of Multiphase Hows has grown tremendously and is now regarded by some as a discipline. Engineering applications, products and processes with particles, bubbles and drops have grown exponentially. An increasing number of conferences, scientific fora and archival journals are committed to the dissemination of information on the flow, heat and mass transfer involving particles, bubbles and drops. Perhaps the most important development of the last thirty years is the emergence of the computer as a tool for scientific inquiry and engineering optimization. Numerical computations and "thought experiments" have almost replaced physical experiments. The literature on computational fluid dynamics with particles, bubbles and drops has grown at an exponential rate in the last twenty five years, giving rise to new results and theories, better understanding of the complex transport processes and has opened new fields of investigation.