科学主义是这样的一种思想，即自然科学是最权威的世界观，也是人类最重要的知识，其高于所有一切其他东西对生活的诠释。「科学主义」这个词首先被社会科学家，如弗里德里希·哈耶克，和科学哲学家，如卡尔·波普尔等使用，用来描述许多科学家所共有的态度和信念，这一信念让自然科学的研究和其所采用的方法终于上升到意识形态的水平。 对科学主义的经典论述，正如物理学家欧内斯特·卢瑟福所言：“除物理，皆集邮。”（"There is physics, and there is stamp-collecting."）

科学主义一词有时在两个方面亦被用作略带贬义的解释：

Scientism is a belief in the universal applicability of the scientific method and approach, and the view that empirical science constitutes the most "authoritative" worldview or the most valuable part of human learning—to the exclusion of other viewpoints. Accordingly, philosopher Tom Sorell provides this definition of scientism: "Scientism is a matter of putting too high a value on natural science in comparison with other branches of learning or culture." It has been defined as "the view that the characteristic inductive methods of the natural sciences are the only source of genuine factual knowledge and, in particular, that they alone can yield true knowledge about man and society". The term "scientism" frequently implies a critique of the more extreme expressions of logical positivism and has been used by social scientists such as Friedrich Hayek, philosophers of science such as Karl Popper, and philosophers such as Hilary Putnam and Tzvetan Todorov to describe (for example) the dogmatic endorsement of scientific methodology and the reduction of all knowledge to only that which is measurable. Philosophers such as Alexander Rosenberg have also appropriated "scientism" as a name for the view that science is the only reliable source of knowledge.