The crystallization of water in clouds plays a key role in weather and climate through its effect on albedo and precipitation. The unassisted, homogeneous nucleation of ice occurs at temperatures lower than -32oC, which are only achieved in high altitude clouds. Ice formation in lower lying, warmer clouds is promoted by atmospheric aerosols. Although the majority of atmospheric aerosols are minerals, the most efficient at forming ice are of biological origin. Ice nucleating bacteria are the most potent ice-nucleating agents in the biosphere and the atmosphere, contributing to cloud glaciation and precipitation, and routinely used for the synthetic production of snow. These bacteria have proteins in their outer membrane that are able to nucleate ice at temperatures as high as -1oC. This presentation will discuss our quest to elucidate the mechanisms by which bacterial proteins and other potent ice nucleants promote water crystallization, what makes them so outstanding, and whether we can design materials that outperform them.