本质主义（Essentialism），又译为精粹主义，是一种认为任何的实体（如一只动物，一群人，一个物理对象，一个观念）都有一些必须具备的本质的观点。这种观点同时会认为无法对现象作出最终解释的理论都是无用的，因为其不能反映客观事实。

「本质主义」这个术语是由卡尔·波普尔第一次提出的，在之前无论是持本质主义观点的学者或是质疑本质主义观点的学者都没有使用这个术语。

本质主义观念在西方的出现可以追溯到柏拉图和亚里士多德。最早为人所知的关于所有的思考和观念背后必定隐藏着一个必要事实（理型）的理论是“柏拉图主义”。亚里士多德的“范畴篇”主张所有的对象都属于某一基本存在，基本存在决定了对象到底是什幺。乔治·莱考夫概括亚里士多德的观点为“那些使得某个事物是什幺的特性，失去了那些特性这些事物就不再是‘那’同一种东西了”。这个观点与“非本质主义”对立。非本质主义声称没有一种特殊的特质是某类型实体必须拥有的。

Essentialism is the view that, for any specific entity (such as an animal, a group of people, a physical object, a concept), there is a set of attributes which are necessary to its identity and function. In Western thought the concept is found in the work of Plato and Aristotle. Platonic idealism is the earliest known theory of how all known things and concepts have an essential reality behind them (an "Idea" or "Form"), an essence that makes those things and concepts what they are. Aristotle's Categories proposes that all objects are the objects they are by virtue of their substance, that the substance makes the object what it is. The essential qualities of an object, so George Lakoff summarizes Aristotle's highly influential view, are "those properties that make the thing what it is, and without which it would be not that kind of thing". This view is contrasted with non-essentialism, which states that, for any given kind of entity, there are no specific traits which entities of that kind must possess.