Contract interpretation is a difficult area. There are numerous principles for the interpretation of contracts. The interpretation principles have been taken into account in almost all the various legal systems. One principle offered for the contract interpretation holds that the written document agreed by both of the parties forms the basis of obligations. In fact, to be drafted contracts need preparatory works that might take some time to be accomplished. The issue is mentioned in Iran’s jurisprudence and law rather vaguely. But, it does not mean that the abovementioned issue has not been given any room in Iran’s laws and jurisprudence. The condition has been born in England’s laws that have thoroughly and comprehensively considered it. The EU laws in the Draft – Common Frame of Reference for a European Private Law investigate the issue. The aforesaid document has well elucidated the condition.