A sickle, bagging hook, reaping-hook or grasshook is a single-handed agricultural tool designed with variously curved blades and typically used for harvesting, or reaping, grain crops or cutting succulent forage chiefly for feeding livestock, either freshly cut or dried as hay. Falx was a synonym but was later used to mean any of a number of tools that had a curved blade that was sharp on the inside edge such as a scythe.

Since the beginning of the Iron Age hundreds of region-specific variants of the sickle have evolved, initially of iron and later steel. This great diversity of sickle types across many cultures can be divided into smooth or serrated blades, both of which can be used for cutting either green grass or mature cereals using slightly different techniques. The serrated blade that originated in prehistoric sickles still dominates in the reaping of grain and is even found in modern grain-harvesting machines and in some kitchen knives.