计算理论（英语：Theory of computation）是数学的一个领域，和计算机有密切关系。其中的理论是现代密码协议、计算机设计和许多应用领域的基础。该领域主要关心三个方面的问题：

计算理论的「计算」并非指纯粹的算术运算（Calculation），而是指从已知的输入透过算法来取得一个问题的答案（Computation），因此，计算理论属于计算机科学和数学。

计算理论早于现代计算机发明前的20世纪便开始了。

In theoretical computer science and mathematics, the theory of computation is the branch that deals with how efficiently problems can be solved on a model of computation, using an algorithm. The field is divided into three major branches: automata theory and language, computability theory, and computational complexity theory, which are linked by the question: "What are the fundamental capabilities and limitations of computers?".