Stipulating a definition
Notwithstanding these difficulties, the term ‘soft law’ remains widely accepted and used by the international legal community, and thus warrants a basic definition.  For the purpose of the present volume, the term soft law is understood to refer to rules (prescribing conduct or otherwise establishing standards) that are in the process of becoming, though may not ultimately become, binding rules of international law, in the form of any of the established sources of international law— customary law, general principles of law, or as an authentic (binding) interpretation of a rule of treaty law.
Of course, any normative statement, irrespective of its source, has some possibility of becoming a rule of international law. However, a normative statement will become a rule of soft law only once it acquires a degree of traction. For the purpose of this study, the term soft law refers to rules that are already in the process of incubation, that are emerging rules of international law, and that are viable candidates for crystallizing into hard law. While non-state actors, such as NGOs and academics, may have an important role to play in identifying and clarifying soft law, this traction must ultimately come in the form of acceptance by the authors of international law—states.
The only criteria used to delimit the concept of soft law for the purposes of the present study are that the content be formulated as a rule and that the rule be in the process of incubation.18 The term ‘soft law instruments’ then may be understood as referring to any instrument with normative content that by its form and provenance provides support sufficient to establish the minimum threshold of traction for at least some of the norms contained therein to be regarded as soft law.
Last, but not least, this volume deals with the roles of soft law in international human rights law. By this we mean the corpus of international and regional principles and standards, binding and non-binding, that govern the protection of human rights, including UN and regional treaties, declarations, and principles adopted by states, relevant case law from international and regional courts, as well as recommendations, observations, and other decisions adopted by human rights organs and monitoring bodies. Related fields such as international criminal law and international humanitarian law are only dealt with in this volume insofar as the issues under examination are linked to international human rights protection.