吸血（Hematophagy，有时拼作haematophagy or hematophagia，来自希腊文，haima“血”，phagein“去吃”）是某些特定动物取食血液的一种行为。由于血液是一种富含营养蛋白和脂质而不需要花费过多努力获得的液体组织，因此特别是在一些小动物例如蠕虫和节肢动物中，吸血演化为一种取食偏好。一些肠道线虫，例如Ancylostomids以吸取肠道中毛细血管的血液为生；还有75%的水蛭种类，例如药用水蛭Hirudo medicinalis，一种自由活动的蠕虫，也是著名的吸血者。还有一些鱼形动物，例如七鳃鳗；和某些哺乳动物，特别是吸血蝙蝠都是典型的吸血者。

Hematophagy (sometimes spelled haematophagy or hematophagia) is the practice of certain animals of feeding on blood (from the Greek words αἷμα haima "blood" and φάγειν phagein "to eat"). Since blood is a fluid tissue rich in nutritious proteins and lipids that can be taken without enormous effort, hematophagy has evolved as a preferred form of feeding in many small animals such as worms and arthropods. Some intestinal nematodes, such as Ancylostomids, feed on blood extracted from the capillaries of the gut and about 75 percent of all species of leeches (e.g. Hirudo medicinalis), a free-living worm, are hematophagous. Some fish, such as lampreys and candirus, and mammals, especially the vampire bats, and birds, such as the vampire finches, hood mockingbirds, the Tristan thrush and oxpeckers, also practise hematophagy.