回流（英语：Reflux）是一种实验操作，用于液态反应体系。有时反应物或溶剂沸点较低，为了不使物料过快气化而损失，通常在反应容器（常为圆底烧瓶）上方安装冷凝管，这样反应物或溶剂蒸气将遇冷回流入反应容器内。通常在加热时还会加入沸石或使用磁力搅拌加热器搅拌，以防暴沸。

Reflux is a distillation technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations. It is also used in chemistry to supply energy to reactions over a long period of time.