Corporate Social Responsibility (CSR) is no longer a theoretical idea; it is now mentioned in treaties, international documents, state regulations and corporate decisions. Accordingly, CSR may be very effective to impact the IL in favour of social claims, using its soft power well established in developed countries and in the international arena. CSR could possibly change the culture which leads to change the legal texts itself, as the many treaties under revision to include more CSR obligations. And it can as well through its influence over the understanding of the existing texts, such as the sustainable development, make a difference in the application of the home state courts and the arbitral tribunals. Accordingly as the CSR is primarily a social concept, about the role of the business within the society, that is when turned into a legal rule it might be quite problematic, but still a very important concept to understand and to spot a light on it, especially in the international arena. This paper will address firstly the definition of CSR, with mentioning the obstacles in the process of its defining. Secondly, the possible nature of the CSR legal rule. Thirdly, how CSR is represented on the international level. Lastly, how the CSR concept is represented in the international law instruments.