Butyllithium may refer to one of 5 isomeric organolithium reagents of which 3 are commonly used in chemical synthesis:
n-Butyllithium, abbreviated BuLi or nBuLi sec-Butyllithium, abbreviated sec-BuLi or sBuLi, has 2 stereoisomers, but is commonly used as racemate tert-Butyllithium, abbreviated tert-BuLi or tBuLi Isobutyllithium