A jinx (also jynx), in popular superstition and folklore, is a curse or the attribute of attracting bad or negative luck.

The word "jynx" meaning the bird wryneck and sometimes a charm or spell has been in use in English since the seventeenth century. The modern spelling and connotations developed late in the nineteenth century. The term "jinx" also commonly arises when one does not want to say something positive about an incomplete or inconclusive situation out of fear of "jinxing it". The superstition goes that speaking positively about one's current situation will cause it to be "jinxed", and things will start to go wrong.

Examples of "jinxing" in the 21st-century press include the suggestion a ship might be "jinxed" was made in connection with two cruise liners after misfortunes, MS Queen Victoria and the Emerald Princess. In the 20th century, the Australian aircraft carrier HMAS Melbourne was sometimes said to be jinxed, having twice struck a friendly ship, with considerable loss of life.

Jinx is also the name given to a game between friends (especially children) when two people say the same word or phrase at the same time and they then call "jinx".