Even though the concept of human rights mainstreaming is not new to public International law, it has recently gained increased recognition as a practical approach for recognizing the linkages between human rights and other social justice issues such as environmental protection. A plenitude of literature have been generated on the need to recognize and enforce human rights standards and norms in a wide range of issues including environment, health, gender, poverty, food, water and refugee protection to mention but a few. Despite the rapid ascendancy of the human rights mainstreaming concept, much attention have not been given to the scope of human rights mainstreaming and the practical aspects of human rights mainstreaming, particularly whether institutions consisting of ‘outsiders' to the human rights epistemic community can interpret and enforce human rights obligation. Put simply, do environmentalists, scientists and outsiders to human rights have the capacity to mainstream human rights? This paper examines the scope and tenets of human rights mainstreaming, it then discusses the practical aspects of mainstreaming human rights into policy making, particularly how epistemic concerns on human rights mainstreaming can be addressed in national and International policy design and implementation.