Kaffir lime is used extensively in Thai cooking. Both the zest and leaves are very useful. The fruit looks like a wrinkled lime, big wrinkles. Thai people believe the juice is excellent hair rinse to prevent hair from falling out. The zest of the lime is a key ingredient in red and green curry pastes.
The juice is used in a few Thai dishes, but the zest is more common.
Recently, Thai growers have developed and started growing a kaffir lime without wrinkles that is easier to pack and ship around the world.