Negotiorum gestio (Latin for "management of business") is a form of spontaneous voluntary agency in which an intervenor or intermeddler, the gestor, acts on behalf and for the benefit of a principal (dominus negotii), but without the latter's prior consent. The gestor is only entitled to reimbursement for expenses and not to remuneration, the underlying principle being that negotiorum gestio is intended as an act of generosity and friendship and not to allow the gestor to profit from his intermeddling. This form of intervention is classified as a quasi-contract and found in civil-law jurisdictions and in mixed systems (e.g. Scots, South African, and Philippine laws).
For example, while you are traveling abroad, a typhoon hits your home town and the roofing of your house is in danger. To avoid the catastrophic situation, your neighbour does something urgently necessary. You are the 'principal' and your neighbour here is the 'gestor', the act of which saved your house is the negotiorum gestio.
It originated as a Roman legal institution in which an individual acted on behalf of another, without his asking and without remuneration. It was considered a part of officium (duty), for instance, to defend a friend's or neighbour's interests while the friend or neighbour was away.
The principal, or dominus, more fully dominus negotiorum dominus rei gestae, is bound to indemnify the gestor for the expenses and liabilities incurred. If the principal fails to do so, there is unjust enrichment, and the gestor then has a claim to bring an action for restitution. In Napoleonic civilian jurisdictions, including Louisiana, the action takes the form of the actio de in rem verso.
Negotiorum gestio is not recognised at common law, despite certain English salvage cases, as well as some cases in equity where trustees were on occasion remunerated for services voluntarily rendered.
It is variously known as follows: