二维双极坐标系是一个正交坐标系。学术界上有三种常用的双极坐标系。除了在这里讨论的坐标系以外，另外两种是双心坐标系与双角坐标系。

这里所要讨论的双极坐标系创建于阿波罗尼奥斯圆。 的等值曲线是圆圈。 的等值曲线也是圆圈。两组圆圈互相垂直相交。双极坐标系有两个焦点 与 ，其直角坐标 通常分别设置为 与 。所以，这两个焦点都处于直角坐标系的 x-轴。

双极坐标系是好几种三维正交坐标系的原始模。往 z-轴方向延伸，则可得到双极圆柱坐标系。绕着 x-轴旋转，即可得到双球坐标系。绕着 y-轴旋转，就可得到圆环坐标系。

Bipolar coordinates are a two-dimensional orthogonal coordinate system. There are two commonly defined types of bipolar coordinates. The first is based on the Apollonian circles. The curves of constant σ and of τ are circles that intersect at right angles. The coordinates have two foci F₁ and F₂, which are generally taken to be fixed at (−a, 0) and (a, 0), respectively, on the x-axis of a Cartesian coordinate system. The second system is two-center bipolar coordinates. There is also a third coordinate system that is based on two poles (biangular coordinates).