累积二烯烃也称为“聚集二烯烃”或“连烯烃”是分子中含有一对相邻碳碳双键（即有一个碳原子通过两个双键与相邻两个碳原子连接）的一类二烯烃。分子中具有超过一对相邻碳碳双键（累积双键）的烯烃则称为“累积多烯烃”。

最简单的累积二烯烃是丙二烯。虽然丙二烯等累积二烯烃是稳定的，但大多数的累积二烯烃皆很不稳定。由它们与氯气等化学物质反应可见，累积二烯烃的活泼程度比一般的烯烃更强，与炔烃相近。因为累积二烯烃具有不稳定性，所以其存在与应用均不甚普遍，现主要用于立体化学方面的研究。

此类二烯烃中，C-C-C键角为180°，两个π键和四个取代基在空间上处于正交，中心碳原子为sp杂化。类似的正交π键出现在烯酮中。

An allene is a compound in which one carbon atom has double bonds with each of its two adjacent carbon centres. Allenes are classified as polyenes with cumulated dienes. The parent compound of allene is propadiene. Compounds with an allene-type structure but with more than three carbon atoms are called cumulenes. Allenes are much more reactive than most other alkenes. For example, their reactivity with gaseous chlorine is more like the reactivity of alkynes than that of alkenes.