在数学中，艾森斯坦级数是一类可直接表成级数的模形式，由费迪南·艾森斯坦首创。对于一般的约化群，罗伯特·朗兰兹也发展了相应的理论。

固定整数 。对上半平面上的复数 ，定义艾森斯坦级数 为

此级数是上半平面上的全纯函数，此外它更是模群 的权 模形式。换言之，若 满足 ，则

This article describes holomorphic Eisenstein series in dimension 1; for the non-holomorphic case see real analytic Eisenstein series and for the higher dimensional case see Siegel Eisenstein series

Eisenstein series, named after German mathematician Gotthold Eisenstein, are particular modular forms with infinite series expansions that may be written down directly. Originally defined for the modular group, Eisenstein series can be generalized in the theory of automorphic forms.