Professional negligence describes a situation where a person exercising a professional skill (such as a solicitor, barrister, accountant, architect, engineer, financial adviser or medical practitioner) fails to perform to the standard of reasonable care and skill expected of a competent member of that profession, causing loss to a client or, in some cases, a third party. It is not generally defined in statute, but developed through case law as a species of negligence and, frequently, breach of contract. Core issues include: the existence and scope of a duty of care, the applicable standard of care (often informed by professional rules and expert evidence), breach, causation and remoteness of damage, and limitation periods. Across England & Wales, Scotland, Northern Ireland and Ireland, usage is broadly consistent, though terminology may differ (for example, “delict” in Scotland). Claims typically arise in professional indemnity litigation, regulatory investigations, and risk management for professional services firms. Professional negligence is central to assessing liability, insurance coverage, settlement strategy and the drafting and enforcement of engagement letters, exclusion clauses and limitation of liability provisions.