In the contract of affreightment, there are many implied obligations applied unless the parties have agreed otherwise. The obligation not to deviate from the agreed route is one of the most important undertakings of the shipowner and the carrier. The doctrine of deviation has been regarded as a long-established doctrine in English maritime law, and its application is still controversial in court’s decisions.From the dissertation for Master of Laws (LL.M.) course, it becomes a highly accessible text for a reader interested in the subject. The book will provide a clear and comprehensive explanation of the doctrine of deviation including its evolution, consequences and recent application under the relevant law. Attention is also devoted to practical issues regarding the liberty to deviate clause and its interpretation by the court. A seperate chapter will deal with the legal effect of deviation on exclusion clauses and the contract of carriage of goods by sea. Throughout, the possible effect of the doctrine in the future will be discussed.