Attention is focused on a suspension of buoyant particles(or droplets) in acontinuous fluid. In the presence of aforce field, gravitational or centrifugal, and exposed toordinary boundary constraints, a variety of fascinatingflows 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 alsointeresting from a broader, academic point of view. Inthese respects, the recent investigations on these flowspatterns, their underlying mechanisms and mathematicalmodeling - have accrued to a significant, relevant body ofknowledge. The main objective of this book is to summarize -in a systematic, coherent and consistent fashion - thetheoretical up to date contributions which seem fundamentalin understanding, simulation and development of the subject.