酮是一类有机化合物，通式RC(=O)R'，其中R和R'可以是相同或不同的原子或官能团。酮的结构特征是具有一个与两个碳原子相连接的羰基（C=O）。 最简单的酮是丙酮。

酮是唯一一类羰基碳直接与两个碳原子相连的有机物。同为羰基化合物的醛、羧酸、酯、酰卤和酰胺中，羰基碳原子的一侧则分别与氢、羟基（氧）、氧、卤素与氮原子相连，不同于酮。

有α-氢的酮可发生酮-烯醇互变异构。酮与强碱反应产生相应的烯醇负离子，反应一般通过烯醇去质子化进行。

“酮”音tóng，在古汉语中有两义：“用马奶制成的酪”与“醋”。近代被用作欧洲语言中此类化合物名的音译。对比：英语ketone（“酮”，< acetone，“丙酮”），以及德语中语义相同的Keton、Aceton。

In chemistry, a ketone (alkanone) /ˈkiːtoʊn/ is an organic compound with the structure RC(=O)R', where R and R' can be a variety of carbon-containing substituents. Ketones and aldehydes are simple compounds that contain a carbonyl group (a carbon-oxygen double bond). They are considered "simple" because they do not have reactive groups like −OH or −Cl attached directly to the carbon atom in the carbonyl group, as in carboxylic acids containing −COOH. Many ketones are known and many are of great importance in industry and in biology. Examples include many sugars (ketoses) and the industrial solvent acetone, which is the smallest ketone.