嗜冷生物是嗜极生物的一种，能够在低温的环境保持生长和繁殖的能力。与之对比的是通常生活在高温环境的嗜热生物。嗜冷细菌在地球上分布很广，因为地球表层很大一片区域的温度都低于15度。它们通常存在于高山或极地土壤、高纬度地区及大洋深处，也存在于被冰、雪、或冰川覆盖的地方。天体生物学家对嗜冷生物很感兴趣，他们试图通过其创建一个关于地外生命可能性的理论。在地球微生物学中，嗜冷细菌也被用来研究微生物在地球化学过程中的活动。

嗜冷生物有着许多不同的新陈代谢方式，包括光合作用、化学自养（也被称为化能自养）、异养以及形成强健的、多样性的种群。大多数嗜冷生物属于细菌或古菌，它们在微生物谱系中也分布广泛。另外，有研究发现在高山雪原低氧地区存在嗜冷的真菌。另外一类真核耐寒生物是雪生藻类，可致西瓜雪的发生。鉴别嗜冷生物主要观察下列特征：脂类细胞膜在化学上能否抵御由极寒带来的硬化，使得其内蛋白质呈现出“大便能力”，在水的熔点以下仍然能够保持其内环境为液态并且保护其DNA免受伤害。

Psychrophiles or cryophiles (adj. cryophilic) are extremophilic organisms that are capable of growth and reproduction in cold temperatures, ranging from −20 °C to +10 °C. Temperatures as low as −15 °C are found in pockets of very salty water (brine) surrounded by sea ice. Psychrophiles are true extremophiles because they adapt not only to low temperatures but often also to further environmental constraints. They can be contrasted with thermophiles, which thrive at unusually hot temperatures. In addition to that, distinctions between mesophilic and psychrophilic cold-shock response, including lack of repression of house-keeping protein synthesis and the presence of cold-acclimation proteins (Caps) in psychrophiles, does exist. The environments they inhabit are ubiquitous on Earth, as a large fraction of our planetary surface experiences temperatures lower than 15 °C. They are present in alpine and arctic soils, high-latitude and deep ocean waters, polar ice, glaciers, and snowfields. They are of particular interest to astrobiology, the field dedicated to the formulation of theory about the possibility of extraterrestrial life, and to geomicrobiology, the study of microbes active in geochemical processes. In experimental work at University of Alaska Fairbanks, a 1000-litre biogas digester using psychrophiles harvested from "mud from a frozen lake in Alaska" has produced 200–300 litres of methane per day, about 20–30% of the output from digesters in warmer climates.