Book excerpt: Bubbles and drops are ubiquitous and are of fundamental importance in various industrial and natural processes. The interaction of bubbles and drops with themselves and the background fluid have major impact on the overall behavior of the flow. Hence the need arises to understand their behavior and to manage them in an efficient way. For almost all conventional applications, the gravitational force is predominantly used to control and manipulate their motion. In the cases where the gravitational force becomes weak, particle control by thermocapillary is a promising alternative. Thus, the thermocapillary which relies on manipulation of bubbles and drops caused by the variation of surface tension with temperature is being studied in many physical, chemical, and engineering disciplines. Some of the prominent applications are reduced gravity materials processing, microelectromechanical devices, microfluidics, mixing enhancement in microdrops and transfer of fluid by thermocapillary. Since in reality the force of gravity is inevitable and not entirely absent the main goal here is to understand the behavior of bubbles/drops under the combined effect of gravity and thermocapillary. To this end, the transient behavior of a drop and a collection of them at low Reynolds number and finite Reynolds number was explored. The study of dynamics of isolated bubbles contributes to the understanding of microstructural response of several industrial applications used in the manipulation of particles. Hence, the multi-bubble interactions were analyzed and their pattern formation was studied. Manipulation of tiny amounts of fluids in the form of drops is a central task in many lab-on-chip applications. This necessitates a fundamental understanding of the behavior of compound drops under thermocapillary conditions. Therefore, preliminary studies were done to decipher the dynamics of compound drops. Direct numerical simulations were used to conduct the study.