Chelating agents are molecules that have the ability to form more than one bond to a metal ion, thereby increasing the stability of the ion complex. The complex is called a chelate, which is a word from the Greek chela, meaning claw. Naturally-occurring chelates transport important nutrients throughout plants and animals, and are important in many life-sustaining reactions. Man-made chelates have both industrial and medical applications.

Perhaps the best known of the chelating agents is ethylenediamine. Its chemical structure is C₂H₈N₂, where H is hydrogen, N is nitrogen, and C is carbon; the subscript "2" indicates how many atoms of each element are present in the molecule. Ethylenediamine is a multidentate chelating agent, specifically a bidentate ligand. That means EDTA can form two bonds; each nitrogen atom can bond with the same metal ion. Depending on how many bonds the metal ion can accept, the ion may form a chelate with one, two, or three ethylenediamine molecules.

Naturally-occurring chelates are necessary for many life-sustaining processes. The vitamin B12-cobalt chelate complex is a dietary requirement in all higher animals. Chlorophyll-magnesium complex is a critical component of photosynthesis. The hemoglobin-iron complex transports oxygen through the blood.

Chelating agents have found uses in industry as detergent additives, stabilizing agents, preservatives, and flavor and color retainers. Ethylenediaminetetraacetic acid (EDTA) is a quadridentate or hexadentate chelating agent; it is capable of forming either four or six bonds with metal ions. EDTA is widely used for enhancing the cleaning power of detergents and soaps by forming chelates with the magnesium and calcium metals in hard water. Chelating agents are also used as color retainers for textile dyes.

EDTA is also used as a food additive. Food spoilage is catalyzed by enzymes that require certain transition metals in order to work. Because of its ability to sequester these metal ions, EDTA deactivates the spoilage enzymes that would otherwise cause the food products to become rancid. EDTA also deactivates the enzymes that cause food to lose color or flavor.

In medicine, EDTA is used to preserve blood by sequestering the calcium ions that cause clotting. Administered intravenously, EDTA is effective in treating cadmium, lead, and iron poisoning by chelating the metal ions and removing them from the blood stream. The bidentate chelating agent dimercaprol removes heavy metal poisons, such as antimony, mercury, and arsenic, by forming sulfur bonds to the metal ions. Subsequently, the sequestered metals are removed from the blood stream and typically eliminated in the urine.