Condensation is the process by which a vapor is converted to its liquid state. Because fo the large internal energy difference between the liquid and vapor states, a significant amount of heat can be released during the condensation process. For this reason the condensation process is used to many thermal systems. In general, a vapor will condense to liquid when it is cooled sufficiently or comes in contact with something (e.g., a solid or another fluid) that is below its equilibrium temperature. This chapter is primarily concerned with convective condensation (condensation of a flowing vapor in a passage) and vapor-space condensation (condensation of stagnate vapor onto a surface). Film condensation occurs when the condensate completely wets the surface in a continuous liquid film and can be associated with either convective or vapor-space condensation. Dropwise condensation - usually associated with vapor-space condensation - occurs when the condensate "beads up" on the surface into drops of liquid as a consequence of the liquid's lack of affinity for the surface. Heat transfer coefficients for dropwise condensation can be one-to-two orders of magnitude greater than that for film condensation. Unfortunately, dropwise condensation is not easily sustained in practice.