In the absence of ice-nucleating particles (INPs) in the atmosphere, cloud droplets freeze homogeneously at a temperature of approximately -35°C. In the presence of INPs, cloud droplets can freeze at higher temperatures. After INPs initiate the formation of ice in cloud droplets, the resulting ice crystals can grow at the expense of liquid droplets since the saturation water vapor pressure is lower over ice than over water. In addition, ice crystals may further grow by collisions until they attain a size that causes them to fall out of the cloud, ultimately contributing to the formation of precipitation. Notably, a substantial fraction of global precipitation proceeds via these processes. INPs also influence the optical properties and lifetimes of clouds, with implications for the cloud albedo effect. Atmospheric ice nucleation thus influences the hydrological cycle and radiative budget, underlining the importance of gaining a comprehensive understanding of the properties, concentration, and sources of INPs in the atmosphere.