Piperazine is an organic compound that consists of a six-membered ring containing two opposing nitrogen atoms. Piperazine exists as small alkaline deliquescent crystals with a saline taste.

The piperazines are a broad class of chemical compounds, many with important pharmacological properties, which contain a core piperazine functional group.

Piperazines were originally named because of their chemical similarity with piperidine, a constituent of piperine in the black pepper plant (Piper nigrum). It is important to note, however, that piperazines are not derived from plants in the Piper genus.

Piperazine is freely soluble in water and ethylene glycol, but insoluble in diethyl ether. It is a weak base with a pK_b of 4.19; the pH of a 10% aqueous solution is 10.8-11.8. Piperazine readily absorbs water and carbon dioxide from the air. Although many piperazine derivatives occur naturally, piperazine itself can be synthesized by reacting alcoholic ammonia with 1,2-dichloroethane, by the action of sodium and ethylene glycol on ethylene diamine hydrochloride, or by reduction of pyrazine with sodium in ethanol.