The parol evidence rule in the South African law of contract consists of two different subrules. The one subrule deals with the extent to which a written contract may be regarded as the sole memorial of its terms and will be referred to as the “integration rule” in this article. Closely related to the integration rule is the so-called “interpretation rule”. The narrow definition of this rule entails that no evidence may be adduced to alter the clear and unambigious meaning of a written or verbal agreement. There is, however, also a wider definition that may be attributed to the interpretation rule, namely that it entails when and to what extent extrinsic evidence may be adduced to explain or alter the wording of a contract. In the past decades, there has been a development in the application of the interpretation rule in the South African law of contract from a strict formalistic textual approach to a more liberal contextual approach in terms of which more extrinsic evidence is allowed in order to interpret the written contract between the parties. In the first part of this article, the subjective and objective approaches to interpretation will be contrasted and the historical background of the interpretation rule will be briefly discussed. There will also be a critical analysis of the development and current application of the interpretation rule in the South African law of contract.