分岔理论或分歧理论（bifurcation theory）是数学中研究一群曲线在本质或是拓扑结构上的改变。一群曲线可能是矢量场内的积分曲线，也可能是一群类似微分方程的解。

分岔（bifurcation）常出现在动态系统的数学研究中，是指系统参数（分岔参数）小而连续的变化，结果造成系统本质或是拓扑结构的突然改变。分岔会出现在连续系统（以常微分方程、时滞微分方程或偏微分方程来描述）或是离散系统中 （以映射来描述）。

bifurcation一词最早是由儒勒·昂利·庞加莱在1885年的论文中提出，这也是第一篇提到类似特性的数学论文，庞加莱后来也为许多不同的驻点命名而且分类。

Bifurcation theory is the mathematical study of changes in the qualitative or topological structure of a given family, such as the integral curves of a family of vector fields, and the solutions of a family of differential equations. Most commonly applied to the mathematical study of dynamical systems, a bifurcation occurs when a small smooth change made to the parameter values (the bifurcation parameters) of a system causes a sudden 'qualitative' or topological change in its behaviour. Bifurcations occur in both continuous systems (described by ODEs, DDEs or PDEs) and discrete systems (described by maps). The name "bifurcation" was first introduced by Henri Poincaré in 1885 in the first paper in mathematics showing such a behavior. Henri Poincaré also later named various types of stationary points and classified them.