The international Commercial Arbitration is a dispute resolution mechanism; thus, it allows the parties to a dispute to settle their affair outside the national courts. On the other hand, lex mercatoria can be defined as a body of rules that encompasses usages and customs that were used by the merchants in the medieval ages, thus the English nomination “merchant law’. After globalization, more specifically in the twentieth century, both above-mentioned concepts have been developed and adopted by most of the legal systems around the world. This paper aims to define lex mercatoria by exploring its’ history, its’ development, and by tackling all its’ elements to study the impact of lex mercatoria’s principles on international commercial arbitration proceedings.