冠醚是一种杂环有机化合物，包含有多个醚基团。最常见的冠醚就是乙撑氧的低聚物，其中重复的单位是乙烯氧基（-CH₂CH₂O- 可看作是环氧乙烷断裂碳氧键后的剩余基团）。这一系列中最重要的是四聚体、五聚体和六聚体。之所以用“冠”来命名，是因为就像皇冠可以戴在头上一样，冠醚能够和一个阳离子成键。在冠醚的命名法中，前面那个数字代表了环内的原子数，第二个数字代表氧的个数。冠醚的概念远远大于乙撑氧的低聚物，另外一个很重要的系列是苯磷二酚的衍生物。

冠醚一般通过卤代烃与醇盐的威廉姆逊合成反应制取。

Crown ethers are cyclic chemical compounds that consist of a ring containing several ether groups. The most common crown ethers are oligomers of ethylene oxide, the repeating unit being ethyleneoxy, i.e., –CH₂CH₂O–. Important members of this series are the tetramer (n = 4), the pentamer (n = 5), and the hexamer (n = 6). The term "crown" refers to the resemblance between the structure of a crown ether bound to a cation, and a crown sitting on a person's head. The first number in a crown ether's name refers to the number of atoms in the cycle, and the second number refers to the number of those atoms that are oxygen. Crown ethers are much broader than the oligomers of ethylene oxide; an important group are derived from catechol.