The doctrine of “unforeseen circumstances” (théorie de l’imprévision, imprevisieleer) allows the revision of a contract when supervening and unforeseeable circumstances occur deeply disturbing the equilibrium of the contract, as a result of what an excessive burden is placed on one of the parties.The doctrine has been rejected in France and Belgium for a long period of time (except in public or administrative contracts), but, more recently, courts seem to recognise that unforeseen circumstances can lead to a renegotiation of the contract.Moreover, the doctrine of unforeseen circumstances is recognised by several recent international instruments (Unidroit Principles, art. 6.2.2 .; the Draft Common Frame of Reference, art. III.-I.110; the Draft Regulation on a Common European Sales Law, art. 89 …)In the last decade, our world experienced some dramatic changes of circumstances ; the best examples are, maybe, the financial crisis and the variation of energy prices.How the doctrine of unforeseen circumstances has apprehended these changes in practice (case law, arbitration awards, renegotiation clauses) will be discussed.