优生学（eugenics）是研究通过受控的选择性生育来改善人种的学说。

优生学的立意是通过人为的手段，对某些特定的人群限制生育，以“改善人类的基因”，本质上与农业的品种改良理论相同，概念与手法则与之相似（差异在于品种改良工程中是选择优势种杂交，而非淘汰不良品种）。但因为其对基因改善只有科学根据，而没有实验佐证因而处于假说地位，另外对某些弱势人群的歧视，使用强制手段，以及二次世界大战时德国纳粹党藉优生学为借口，屠杀犹太人等缘故，在战后被普遍认为是伪科学或是道德疑虑。今天，一些优生学的部分学说在一些国家得以保留甚至推广（如新加坡、韩国），同时这种做法在学术界有争议。优生学提倡利用应用科学中的生物社会运动来改进人种的基因，从而组成一个优秀的人口。优生学也是一种社会哲学，它提倡通过提高繁殖能力和创造更优秀的下一代和减少不被大众所接受的人种的繁殖能力来改善人类遗传特征，从而改变人种。

Eugenics (/juːˈdʒɛnɪks/; from Greek εὐγενής eugenes "well-born" from εὖ eu, "good, well" and γένος genos, "race, stock, kin") is a set of beliefs and practices that aims at improving the genetic quality of the human population. It is a social philosophy advocating the improvement of human genetic traits through the promotion of higher rates of sexual reproduction for people with desired traits (positive eugenics), or reduced rates of sexual reproduction and sterilization of people with less-desired or undesired traits (negative eugenics), or both. Alternatively, gene selection rather than "people selection" has recently been made possible through advances in gene editing (e.g. CRISPR). The exact definition of eugenics has been a matter of debate since the term was coined. The definition of it as a "social philosophy"—that is, a philosophy with implications for social order—is not universally accepted, and was taken from Frederick Osborn's 1937 journal article "Development of a Eugenic Philosophy".