拟共形映射又称拟保角映射，原本是复分析中的一套技术手段，现已发展为一套独立学科。其定义如下。

固定实数 。

设 为平面上的开子集，连续可微函数 保持定向。若在每一点上其导数 将圆映至离心率小于等于 之椭圆，则称 为 -拟共形映射。由此可见共形映射是 -拟共形映射。

若存在 使 为拟共形映射，则称 为拟共形映射。

In mathematical complex analysis, a quasiconformal mapping, introduced by Grötzsch (1928) and named by Ahlfors (1935), is a homeomorphism between plane domains which to first order takes small circles to small ellipses of bounded eccentricity.

Intuitively, let f : D → D′ be an orientation-preserving homeomorphism between open sets in the plane. If f is continuously differentiable, then it is K-quasiconformal if the derivative of f at every point maps circles to ellipses with eccentricity bounded by K.