This article examines the leading principles governing interpretation of written contracts under English law. This is a comprehensive and incisive analysis of the current law and of the relevant doctrines, including the equitable principles of rectification, as well as the powers of appeal courts or of the High Court when hearing an appeal from an arbitral award. The topic of interpretation of written contracts is fast-moving. It is of fundamental importance because this is the most significant commercial focus for dispute and because of the number of cross-border transactions to which English law is expressly applied by businesses.