An ombudsman (conventional English plural: ombudsmen) is a person who acts as a trusted intermediary between either the state (or elements of it) or an organization, and some internal or external constituency, while representing not only but mostly the broad scope of constituent interests. An indigenous Danish, Norwegian and Swedish term, Ombudsman is etymologically rooted in the Old Norse word umboðsmaðr, essentially meaning "representative". In its most frequent modern usage, an ombudsman is an official, usually appointed by the government or by parliament but with a significant degree of independence, who is charged with representing the interests of the public by investigating and addressing complaints reported by individuals. Modern variations of this term include "ombud", "ombuds", "ombudsperson", or "ombudswoman".

Whether appointed by the legislature, the executive, or an organization (or, less frequently, elected by the constituency), the typical duties of an ombudsman are to investigate constituent complaints and attempt to resolve them, usually through recommendations (binding or not) or mediation. Ombudsmen sometimes also aim to identify systemic issues leading to poor service or breaches of people's rights. At the national level, most ombudsmen have a wide mandate to deal with the entire public sector, and sometimes also elements of the private sector (for example, contracted service providers). In some cases, there is a more restricted mandate, for example with particular sectors of society. More recent developments have included the creation of specialised Children's Ombudsman and Information Commissioner agencies.