N-Chlorosuccinimide (NCS) is the organic compound with the formula C2H4(CO)2NCl.

[3] NCS is related to succinimide, but with N-Cl in place of N-H.

The N–Cl bond is highly reactive, and NCS functions as a source of "Cl+".

NCS is produced from succinimide by treatment with Cl+ sources, such as sodium hypochlorite (bleach), and t-butylhypochlorite, and even chlorine.

Aniline and mesitylene are converted to the respective chlorinated derivatives.