数学上，一个公理系统（或称公理化系统，公理体系，公理化体系）是一个公理的集合，从中一些或全部公理可以一并用来逻辑地导出定理。一个数学理论由一个公理系统和所有它导出的定理组成。一个完整描述出来的公理系统是形式系统的一个特例；但是通常完全角式化的努力仅带来在确定性上递减的收益，并让人更加难以阅读。所以，公理系统的讨论通常只是半角式化的。一个形式化理论通常表示一个公理系统，例如在模型论中表述的那样。一个形式化证明是一个证明在形式化系统中的表述。

In mathematics, an axiomatic system is any set of axioms from which some or all axioms can be used in conjunction to logically derive theorems. A mathematical theory consists of an axiomatic system and all its derived theorems. An axiomatic system that is completely described is a special kind of formal system. A formal theory typically means an axiomatic system, for example formulated within model theory. A formal proof is a complete rendition of a mathematical proof within a formal system.