威廉·瑟斯顿（Thurston）的几何化猜想（geometrization conjecture）指的是，任取一个紧致（可能带边）的三维流形尽量作连通和以使其成为尽可能简单的三维流形的连通和，对于带边流形可能还需要沿着一些圆盘继续切割，有唯一的方法沿着一些环面（如果是带边流形还要加上平环）割开得到尽可能简单的若干小块，这些小块均为八种标准几何结构之一。

八种标准几何结构均为完备的黎曼度量，这些几何结构在某种意义上是比较“好”的，例如体积有限、“直线”都可无限延伸等等。

In mathematics, Thurston's geometrization conjecture states that certain three-dimensional topological spaces each have a unique geometric structure that can be associated with them. It is an analogue of the uniformization theorem for two-dimensional surfaces, which states that every simply-connected Riemann surface can be given one of three geometries (Euclidean, spherical, or hyperbolic). In three dimensions, it is not always possible to assign a single geometry to a whole topological space. Instead, the geometrization conjecture states that every closed 3-manifold can be decomposed in a canonical way into pieces that each have one of eight types of geometric structure. The conjecture was proposed by WilliamThurston (1982), and implies several other conjectures, such as the Poincaré conjecture and Thurston's elliptization conjecture.