The legal operationalisation of ecological sustainability concerns all levels of legal control. The ensuring of full biodiversity is an indispensible component of ecological sustainability. At the same time, biodiversity losses continue to be a serious problem in many regions of the world. The international community has responded to this dilemma by strengthening international biodiversity law as well as agreeing upon a particular biodiversity target. The aim is to reduce biodiversity losses at all levels by the year 2010. From a legal point of view this seems unproblematic. When, however, the international legal order is viewed as an overarching control system, composed of several multi-levelled and interacting international and national legal systems (controlling programs), questions on whether the order can actually work for biodi-versity seem inevitable. By applying and developing further environmental law methodology (ELM) the study argues that some fundamental principles of the international legal order are either diminishing or counteracting the possible realisation of ecological sustainabil-ity and the 2010 biodiversity target of halting and reversing the biodiversity loss. This, as will be argued, is due to rule of law and to how the default actually functions in the international legal system. In line with the above, the prime objective of the study is to develop and elaborate a theory framework on which the theory of the significance of the default is based; second, to evaluate and discuss some fundamen-tal principles of the international legal order and international biodiversity law in the light of the theory, and finally to evaluate and discuss the possible realisation of ecological sustainability and the 2010 target. The study’s method is to a certain extent pluralistic, but it is basically an adapted version of ELM.