The Kaffir lime, also known as Kieffer lime, Makrut, or Magrood, is a Southeast Asian citrus plant with very pungent leaves. The green lime fruits are distinguished by their bumpy exterior and their small size (approx. 4 cm wide), and the hourglass-shaped leaves (actually, the leaf and the leaf-shaped stem or phyllode) are widely used in Thai cuisine and Lao cuisine.

Kaffir lime leaves are also popular in the west of Cambodia, but less so in Vietnam. Malay and Indonesian (especially, Balinese; see also Indonesian bay leaf) cuisines use them sporadically with chicken and fish.
The leaves can be used fresh or dried, and can be stored frozen.
Although the most common product of the kaffir lime tree is its leaves (which impart a sharp lime/neroli flavour to Thai dishes such as tom yum, and to Indonesian food such as sayur assam - literally sour vegetables), the juice and rinds of the small, dark green gnarled fruit (known as jeruk obat - literally medicine citrus) are used in traditional Indonesian medicine.

As for the zest, it is widely used in creole cuisine and to impart flavor to "arranged" rums in the Réunion island and Madagascar.