在生物化学和药理学中，配体（英语：ligand）是指一种能与受体结合以产生某种生理效果的物质。在蛋白质—配体复合物中，配体通常是与靶蛋白特定结合位点相连的信号触发分子。而在DNA—配体复合物中，与DNA双链相连的配体在一般情况下可以是任何的小分子或离子甚至是蛋白质。

配体与受体的连接由诸如离子键的化学键或氢键、范德华力等分子间作用力维系。它们的连接过程通常是可逆的，配体与受体之间形成的真正难以断开的共价键在生物界是相当罕见的。值得注意的是，生物化学中的配体和化学中定义的配体（比如铜氨络离子中，氨是铜离子的配体）并无实际联系，配体未必要结合在金属原子上。

In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In protein-ligand binding, the ligand is usually a molecule which produces a signal by binding to a site on a target protein. The binding typically results in a change of conformation of the target protein. In DNA-ligand binding studies, the ligand can be a small molecule, ion, or protein which binds to the DNA double helix. The relationship between ligand and binding partner is a function of charge, hydrophobicity, and molecular structure. The instance of binding occurs over an infinitesimal range of time and space, so the rate constant is usually a very small number.