Attention is focused on a suspension of buoyant particles§(or droplets) in acontinuous fluid. In the presence of a§force field, gravitational or centrifugal, and exposed to§ordinary boundary constraints, a variety of fascinating§flows can be obtained. These motions are essential ingre-§dients in the widely used separation technology, where im-§provedand new designs may be beneficial, but they are also§interesting from a broader, academic point of view. In§these respects, the recent investigations on these flows§patterns, their underlying mechanisms and mathematical§modeling - have accrued to a significant, relevant body of§knowledge. The main objective of this book is to summarize -§in a systematic, coherent and consistent fashion - the§theoretical up to date contributions which seem fundamental§in understanding, simulation and development of the subject.