In the United Kingdom and in some Commonwealth countries, a King's Counsel (post-nominal initials KC) during the reign of a king, or Queen's Counsel (post-nominal initials QC) during the reign of a queen, is a lawyer (usually a barrister or (in Scotland) advocate) who is typically a senior trial lawyer. Technically appointed by the monarch of the country to be one of 'His [Her] Majesty's Counsel learned in the law', the position originated in England and Wales. Some Commonwealth countries have either abolished the position, or renamed it so as to remove monarchical connotations, for example, 'Senior counsel' or 'Senior Advocate'.

Appointment as King's Counsel is an office, conferred by the Crown, that is recognised by courts. Members have the privilege of sitting within the inner bar of court. As members wear silk gowns of a particular design (see court dress), appointment as King's Counsel is known informally as receiving, obtaining, or taking silk and KCs are often colloquially called silks. Appointments are made from within the legal profession on the basis of merit rather than a particular level of experience. Successful applicants tend to be barristers, or (in Scotland) advocates with 15 years of experience or more.