A lady-in-waiting or court lady is a female personal assistant at a court, attending on a royal woman or a high-ranking noblewoman. Historically, in Europe, a lady-in-waiting was often a noblewoman but of lower rank than the woman to whom she attended. Although she may either have received a retainer or may not have received compensation for the service she rendered, a lady-in-waiting was considered more of a secretary, courtier, or companion to her mistress than a servant.

In other parts of the world, the lady-in-waiting, often referred to as palace woman, was in practice a servant or a slave rather than a high-ranking woman, but still had about the same tasks, functioning as companion and secretary to her mistress. In courts where polygamy was practised, a court lady was formally available to the monarch for sexual services, and she could become his wife, consort, courtesan, or concubine.

Lady-in-waiting or court lady is often a generic term for women whose relative rank, title, and official functions varied, although such distinctions were also often honorary. A royal woman may or may not be free to select her ladies, and, even when she has such freedom, her choices are usually heavily influenced by the sovereign, her parents, her husband, or the sovereign's ministers (for example, in the Bedchamber crisis).