Obligatio consensu

''Consensu'' or ''obligatio consensu'' or ''obligatio consensu contracta'' or ''obligations ex consensu'' or ''contractus ex consensu'' or ''contracts consensu'' or ''consensual contracts'' or obligations by consent are, in Roman law, those contracts which do not require formalities.

These contracts were formed by the mere consent of the parties, there being no requirement for any writing or formalities, nor even for the presence of the parties. Such contracts were bilateral, that is to say, they bound both parties to them. Such contracts depended on the ''ius gentium'' for their validity and were enforced by praetorian actions, ''bonae fidei'', and not by actions ''stricti juris'', as were the contracts which depended on the classical ''ius civile'' of Rome. The term ''consensual'' does not mean that the consent of the parties is more emphatically given than in other forms of agreement, but it indicates that the obligation is annexed at once to the consensus, in the contracts of this type.

Justinian's Institutes classify the following contracts as ''ex consensu'': ''emptio venditio'', ''locatio conductio'', ''societas'' and ''mandatum''. Provided by Wikipedia