在物理学里，多极展开方法广泛应用于涉及于质量分布产生的重力场、电荷分布产生的电势或电场、电流分布产生的磁矢量势和磁场、电磁波的传播等等问题。使用多极展开，重力场或电势等等，都可以表达为单极项目、偶极项目、四极项目、八极项目等等的叠加。一个典型范例是，从原子核的外部多极矩与电子轨域的内部多极矩之间的交互作用能量，计算求得原子的原子核外多极矩。由于从原子核的外多极矩可以给出原子核内部的电荷分布，物理学者可以研究原子核的形状。

做理论运算时，在允许误差范围内，时常可以只取多极展开的最低级的几个非零项目，忽略其它项目，因为它们的数值超小。

A multipole expansion is a mathematical series representing a function that depends on angles — usually the two angles on a sphere. These series are useful because they can often be truncated, meaning that only the first few terms need to be retained for a good approximation to the original function. The function being expanded may be complex in general. Multipole expansions are very frequently used in the study of electromagnetic, gravitational fields and aeroacoustics, where the fields at distant points are given in terms of sources in a small region . The multipole expansion with angles is often combined with an expansion in radius. Such a combination gives an expansion describing a function throughout three-dimensional space.