This chapter reviews how soft law has become a significant part of the evolutionary system of environmental law-making for three main reasons. First, it may be easier to reach agreement when the form is non-binding. The soft law approach allows states to tackle a problem collectively at a time when they do not want to shackle their freedom of action too firmly. Secondly, soft law instruments will normally be easier to supplement, amend, or replace than treaties, since all that is required is the adoption of a new resolution by the relevant international institution. Thirdly, it may be easier for some states to adhere to non-binding instruments because they can avoid the domestic treaty ratification process, and perhaps escape democratic accountability for the policy to which they have agreed. Whether soft law instruments have the same effect as a treaty, or any legal effect at all, will depend on the particular instrument and its relationship to customary international law and to specific treaties.