In practice, apparent authority (or ostensible authority) describes when a principal is bound by an agent’s act because the principal’s words, conduct or the agent’s position reasonably led a third party to believe the agent had authority, even if no actual authority existed.A case-law doctrine in agency law (see Freeman & Lockyer; Armagas v Mundogas), it turns on: a representation or holding out attributable to the principal (including by appointing someone to a role such as managing director); the third party’s reasonable, good-faith reliance; and a transaction of a kind ordinarily within that role’s scope. An agent’s assertion is not enough. If the third party knows of limits, or is put on inquiry, the principal is not bound.For companies, this operates alongside statutory protections for persons dealing with a company in good faith (Companies Act 2006, section 40; comparable protections under Ireland’s Companies Act 2014). For partnerships, the Partnership Act 1890 attributes acts of a partner in the usual course of business to the firm unless the third party knows of a lack of authority.Usage and effect are broadly consistent across England & Wales, Scotland, Northern Ireland and Ireland, and central to transactional risk and due diligence.