In chemistry, acylation is a broad class of chemical reactions in which an acyl group (R−C=O) is added to a substrate. The compound providing the acyl group is called the acylating agent. The substrate to be acylated and the product include the following:
A particularly common type of acylation is acetylation, the addition of the acetyl group. Closely related to acylation is formylation, which employ sources of "HCO+ in place of "RCO+".