在生物学和生态学中，绝灭或称灭绝、绝种（英语：Extinction）是指一个或一族物种的消失。灭绝的瞬间通常指该物种最后一个个体的死亡，没有子孙后代。

在有性繁殖的物种中，当一个物种只有一个体，或者只有一个性别的个体，那幺这个物种的灭绝是不可避免的。

在地质时代，灭绝是一个司空见惯的事件，物种通过物种的形成而出现，通过灭绝而消失。

物种灭绝在早期并不是一个被普遍接受的概念，因为很易把「其所有后代都死光」混淆，那么除了最原始的生物外，所有前现代的生物死绝，就不可能进化成现代的生物。现在的意思是指名和原始的外观相似，可被识别为同一物种的后代死绝，而存活的后代是透过物种的形成的方式在现代生存。

In biology and ecology, extinction is the end of an organism or of a group of organisms (taxon), normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" (typically in the fossil record) after a period of apparent absence.