The Enzyme-Linked Immunosorbent Assay (ELISA) is a laboratory technique used to detect and quantify proteins, hormones, or antibodies in a sample. It works by immobilizing an antigen on a solid surface, then adding a specific antibody linked to an enzyme. When a substrate for the enzyme is added, a measurable signal, often a color change, indicates the presence and amount of the target substance. ELISA is widely used in various fields, including clinical diagnostics, research, and quality control. It is particularly valuable for detecting diseases, such as those caused by viruses or bacteria, and for measuring levels of hormones or allergens in biological samples.