二名法（英语：Binomial nomenclature，binominal nomenclature或binary nomenclature），又称双名法，依照生物学上对生物种类的命名规则，所给定的学名之形式，自林奈《植物种志》(1753年， Species Plantarum)后，成为种的学名形式。正如“二名”字面的意涵，每个物种学名的由两个部分构成：属名和种加词（种小名）。属名由拉丁语法化的名词形成，但是它的字源可以是来自拉丁词或希腊词或拉丁化的其他文本构成，首字母须大写；种加词是拉丁文中的形容词，首字母不大写。通常在种加词的后面加上命名人及命名时间，如果学名经过改动，则既要保留最初命名人，并加上改名人及改名时间。命名人、命名时间一般可省略。习惯上，在科学文献的印刷出版时，学名之引用常以斜体表示，或是于正排体学名下加底线表示。

Binomial nomenclature (also called binominal nomenclature or binary nomenclature) is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomial name (which may be shortened to just "binomial"), a binomen or a scientific name; more informally it is also called a Latin name. The first part of the name identifies the genus to which the species belongs; the second part identifies the species within the genus. For example, humans belong to the genus Homo and within this genus to the species Homo sapiens. The formal introduction of this system of naming species is credited to Swedish natural scientist Carl Linnaeus (author abbrv. L.), effectively beginning with his work Species Plantarum in 1753.