A fiduciary relationship arises where one person undertakes to act for, or on behalf of, another in circumstances that give rise to trust and confidence, and a duty of loyalty. It typically requires the fiduciary to prioritise the beneficiary’s interests over their own, avoid conflicts of interest, not profit from their position without informed consent, and act in good faith.In practice, fiduciary relationships commonly include trustee–beneficiary, director–company, solicitor–client and agent–principal. Courts in England and Wales, Scotland, Northern Ireland and Ireland have developed the concept mainly through case law rather than exhaustive statutory definition, and may recognise fiduciary duties in other relationships depending on the facts.Key legal consequences include strict duties of loyalty, duties to account for unauthorised profits, and remedies such as constructive trusts, equitable compensation or account of profits. Breach of fiduciary duty frequently arises in company law, trusts, partnerships, financial services, and professional negligence claims.Usage and core principles are broadly consistent across the UK and Ireland, though terminology (for example, “equitable” versus “fiduciary” obligations) and doctrinal framing may vary slightly between common law and mixed systems, particularly in Scots law.