Abstract: This study aims to highlight the spread use of modification clauses in market transactions, and the negative consequences resulting from this use through the representation of the interests of one contracting party to the detriment of the interests of the other. The study begins with focusing the definition of modification clauses and detects also many examples which are selected from the market. It then moves to examine how the general principles of contract law in Palestine and English law recognize the use of these terms to finally conclude the need to legislate special rules to deal with the use of these terms.