To make a pinky promise, or pinky swear, is a traditional gesture most commonly practiced amongst children involving the locking of the pinkies of two people to signify that a promise has been made. The gesture is taken to signify that the person can break the finger of the one who broke the promise. The tradition appears to be a relatively modern invention, possibly as a continuation of older finger traditions.^[1][2]

In North America, it is most common amongst school-aged children or adults and close friends and has existed since at least 1860, when the Dictionary of Americanisms listed the following accompanying promise:

Pinky, pinky bow-bell,
Whoever tells a lie
Will sink down to the bad place
And never rise up again.^[3]

Pinky swearing has origins in Japan from 1600 to 1803, where it is called yubikiri (指切り, "finger cut-off") and often additionally confirmed with the vow "Pinky swear, whoever lies will be made to swallow a thousand needles." (指切り拳万、嘘ついたら針千本呑ます, "Yubikiri genman, uso tsuitara hari senbon nomasu").^[4]

Recently, in South Korea, the hooked pinky has been followed by a "seal", wherein the thumbs touch each other while the pinkies are still hooked.^[5][6]

In Taiwan, stamping after hooking pinkies has been commonplace for over 30 years.

In Belfast, Northern Ireland it is referred to as a "piggy promise".^[1]

In Italy, a similar tradition is called "giurin giurello" or "giurin giuretto/-a".

In Maharashtra (India), this concept similarly using Marathi calls this "Gatti fu".

There is also another pinky swear promise made between children in the Isle of Man. It goes: "Make friends, make friends, Never ever break friends, If you do, You'll catch the flu, And that will be the end of you!"