Mankind's first tool a knife is a tool with a cutting edge or blade attached to a handle. Kives were used at least two-and-a-half million years ago. Originally made of rock, bone, flint, and obsidian, over the centuries, in step with improvements in metallurgy or manufacture, knife blades have been made from bronze, copper, iron, steel, ceramics, and titanium. Most modern knives have either fixed or folding blades; blade patterns and styles vary by maker and country of origin.

Knives can serve various purposes. Hunters use a hunting knife, soldiers use the combat knife, scouts, campers, and hikers carry a pocket knife; there are kitchen knives for preparing foods (the chef's knife, the paring knife, bread knife, cleaver), table knives (butter knives and steak knives), weapons (daggers or switchblades), knives for throwing or juggling, and knives for religious ceremony or display (the kirpan).