The Fairbairn–Sykes fighting knife is a double-edged fighting knife resembling a dagger or poignard with a foil grip. It was developed by William Ewart Fairbairn and Eric Anthony Sykes in Shanghai based on ideas that the two men had while serving on the Shanghai Municipal Police in China before World War II.

A dagger is a fighting knife with a very sharp point and usually one or two sharp edges, typically designed or capable of being used as a cutting or thrusting weapon. Daggers have been used throughout human history for close combat confrontations, and many cultures have used adorned daggers in ritual and ceremonial contexts. The distinctive shape and historic usage of the dagger have made it iconic and symbolic. A dagger in the modern sense is a weapon designed for close-proximity combat or self-defense; due to its use in historic weapon assemblages, it has associations with assassination and murders. Double-edged knives, however, play different sorts of roles in different social contexts.