重整化（Renormalization）是量子场论、场的统计力学和自相似几何结构中解决计算过程中出现无穷大的一系列方法。

在量子场论发展的早期，人们发现许多圈图（即微扰展开的高阶项）的计算结果含有发散（即无穷大）项。重整化是解决这个困难的一个方案。一个理论如果只有有限种发散项，则可以在拉氏量中引进有限数目的项来抵消这些无穷大项，这种情形被称为可重整。反之，如果理论中有无限种发散项，则称为不可重整。

可重整化曾被认为一个场论所必需满足的自洽性要求。它在量子电动力学和量子规范场论的发展过程中起过重要的作用。粒子物理的标准模型也是可重整的。

In quantum field theory, the statistical mechanics of fields, and the theory of self-similar geometric structures, renormalization is any of a collection of techniques used to treat infinities arising in calculated quantities.

Renormalization specifies relationships between parameters in the theory when the parameters describing large distance scales differ from the parameters describing small distances. Physically, the pileup of contributions from an infinity of scales involved in a problem may then result in infinities. When describing space and time as a continuum, certain statistical and quantum mechanical constructions are ill-defined. To define them, this continuum limit—the removal of the "construction scaffolding" of lattices at various scales—has to be taken carefully, as detailed below. Renormalization procedures are based on the requirement that certain physical quantities are equal to the observed values.