适体 (源自拉丁文「aptus」表示”适合”的意思,和希腊文「meros」表示”部位”的意思)是指与特定的目标分子结合的寡聚核酸或是 肽链。适体常常从大量的随机串行被挑选出来,但自然的适体依旧存在如核糖开关中。适体可以用在学术研究亦可以当作大分子药物应用在临床诊断上。在适体的目标分子存在的情况下，适体能与核酶结合并进行自我剪切的动作，这些复合物能应用在研究、工业与临床诊断上。

有高度专一性的适体能如下分类:

Aptamers (from the Latin aptus - fit, and Greek meros - part) are oligonucleotide or peptide molecules that bind to a specific target molecule. Aptamers are usually created by selecting them from a large random sequence pool, but natural aptamers also exist in riboswitches. Aptamers can be used for both basic research and clinical purposes as macromolecular drugs. Aptamers can be combined with ribozymes to self-cleave in the presence of their target molecule. These compound molecules have additional research, industrial and clinical applications.