In the previous chapter, we discussed how aqueous solution droplets are activated into cloud droplets. During the entire growth process, the droplet grows by taking up water molecules from the supersaturated vapor phase. Water vapor molecules are transported via diffusion towards the droplet surface where condensation takes place. This process is called diffusional or condensational growth. It will be detailed in this chapter along with the fundamental principles, such as Fick’s law and heat conduction, to derive rigorous mathematical descriptions of diffusional growth. Because diffusional growth alone does not lead to the formation of raindrops and precipitation, we discuss other relevant microphysical processes occurring in warm clouds, like droplet growth by collision–coalescence. Coalescence is a special case of coagulation that involves two liquid hydrometeors. To understand the collision–coalescence process, the settling of cloud droplets and other hydrometeors found in warm clouds is discussed, and formulations for their terminal velocities are presented. Evaporation and break-up of raindrops, which limit raindrops to a maximum radius of around 5 mm, are also discussed.