在福利经济学中，次优理论（英语：Theory of the second best），又称次佳理论，是用来处理当一项或多项帕雷托最适条件无法达成时，所发生的经济状况。这个理论最早在理乍得·利普西（Richard Lipsey）与凯尔文·兰开斯特（Kelvin Lancaster）在1956年提出的论文〈次优的一般理论〉（The General Theory of Second Best）中被提出。

In economics, the theory of the second best concerns the situation when one or more optimality conditions cannot be satisfied. The economists Richard Lipsey and Kelvin Lancaster showed in 1956, that if one optimality condition in an economic model cannot be satisfied, it is possible that the next-best solution involves changing other variables away from the values that would otherwise be optimal. Politically, the theory implies that if it is infeasible to remove a particular market distortion, introducing a second (or more) market distortion may partially counteract the first, and lead to a more efficient outcome.