Bubbles and drops are encountered in our day-to-day life. They also appear in a variety of engineering and materials processing applications. The word bubble represents an object that contains a gas or vapour and the word drop is used to designate an object that contains liquid. In this review, we shall frequently use the term drop to refer to both types of objects. In some cases, it is desirable to have a collection of bubbles in a material as in polymer foams. In other situations, such as when growing a crystal, we wish to produce a material that is free of such inclusions. Stable suspensions of drops are necessary for producing a composite material by cooling a liquid containing more than one component through a miscibility gap into a solid. On the other hand, after contacting one liquid dispersed as drops with another to exchange some component between them, it is necessary to settle out the drops and separate the two phases in mass transfer applications.