狄尔斯–阿尔德反应（英语：Diels–Alder reaction）又叫Diels–Alder反应、双烯加成反应，其中狄尔斯又译作第尔斯–阿尔德又译作阿德尔、阿德耳。狄尔斯–阿尔德反应是一种有机反应（具体而言是一种环加成反应），共轭双烯与取代烯烃（一般称为亲双烯体）反应生成取代环己烯。即使新形成的环之中的一些原子不是碳原子，这个反应也可以继续进行。一些狄尔斯–阿尔德反应是可逆的，这样的环分解反应叫做逆狄尔斯–阿尔德反应或逆Diels–Alder反应（retro-Diels–Alder）。

1928年德国化学家奥托·迪尔斯和他的学生库尔特·阿尔德首次发现和记载这种新型反应，他们也因此获得1950年的诺贝尔化学奖。

The Diels–Alder reaction is an organic chemical reaction (specifically, a [4+2] cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. It was first described by Otto Diels and Kurt Alder in 1928, for which work they were awarded the Nobel Prize in Chemistry in 1950. The Diels–Alder reaction is particularly useful in synthetic organic chemistry as a reliable method for forming 6-membered systems with good control over regio- and stereochemical properties. The underlying concept has also been applied to other π-systems, such as carbonyls and imines, to furnish the corresponding heterocycles, known as the hetero-Diels–Alder reaction. Diels–Alder reactions can be reversible under certain conditions; the reverse reaction is known as the retro-Diels–Alder reaction.