Archaeological evidence suggests that people have been using iron for at least 5000 years. Iron is the cheapest and one of the most abundant of all metals, comprising nearly 5.6% of the earth's crust and nearly all of the earth's core. Iron is primarily obtained from the minerals hematite (Fe₂O₃) and magnetite (Fe₃O₄). The minerals taconite, limonite (FeO(OH)·nH₂O) and siderite (FeCO₃) are other important sources.

Huge amounts of iron are used to make steel, an alloy of iron and carbon. Steel typically contains between 0.3% and 1.5% carbon, depending on the desired characteristics. The addition of other elements can give steel other useful properties. Small amounts of chromium improves durability and prevents rust (stainless steel); nickel increases durability and resistance to heat and acids; manganese increases strength and resistance to wear; molybdenum increases strength and resistance to heat; tungsten retains hardness at high temperatures; and vanadium increases strength and springiness. Steel is used to make paper clips, skyscrapers and everything in between.

In addition to helping build the world around us, iron helps keep plants and animals alive. Iron plays a role in the creation of chlorophyll in plants and is an essential part of hemoglobin, the substance that carries oxygen within red blood cells. Iron sulfate (FeSO₄) is used to treat the blood disease anemia.