在生物学中，再生是指由基因组、细胞、微生物和生态系统对在自然环境下所造成的自身损伤的一种重建、恢复和发育的过程。从细菌到人类，任何物种都有再生能力。再生可以是完全性再生，即损伤后由周围同种细胞来修复，或者是不完全性再生，即损伤后坏死组织由纤维结缔组织来修复。在再生开始阶段，再生是由DNA合成的分子过程介导的。生物学中的再生主要是指多细胞生物通过修复及保持他们的生理和形态的完整性的一种性状。再生从根本上说是由基因调节的无性细胞过程。再生不同于繁殖。举例来说，水螅通过出芽生殖的方式进行再生而不是繁殖。

In biology, regeneration is the process of renewal, restoration, and growth that makes genomes, cells, organisms, and ecosystems resilient to natural fluctuations or events that cause disturbance or damage. Every species is capable of regeneration, from bacteria to humans. Regeneration can either be complete where the new tissue is the same as the lost tissue, or incomplete where after the necrotic tissue comes fibrosis. At its most elementary level, regeneration is mediated by the molecular processes of gene regulation. Regeneration in biology, however, mainly refers to the morphogenic processes that characterize the phenotypic plasticity of traits allowing multi-cellular organisms to repair and maintain the integrity of their physiological and morphological states. Above the genetic level, regeneration is fundamentally regulated by ****ual cellular processes. Regeneration is different from reproduction. For example, hydra perform regeneration but reproduce by the method of budding.