Due Diligence in International Law

Abstract: Due diligence is a quite old concept. Already in the end of the 19th century, it was discussed in matters concerning neutrality. Since then, the concept of due diligence has extended to other areas of law. The fields of international law under examination in this thesis are international environmental law, the protection of the marine environment, diplomatic law, the treatment of aliens and the security of foreign States (terrorism). The intention with the thesis was to describe the possible existence of due diligence in these various fields of law and make a comparison of the concept between the areas. The main question was whether due diligence has a uniform content and function or whether any differences can be displayed. Due diligence is a generally accepted concept in international environmental law. States must behave in such a way as to ensure that no damage will occur to the environment of other States or other areas, as a result of the activities under their jurisdiction and control. Thus, the necessary measures should be taken in order to prevent environmental harm. Due diligence has a comparable content in the field of marine protection. States are also obliged to act appropriately to maintain the inviolability of the diplomatic agent and the diplomatic mission. The receiving State must therefore identify, understand, and manage possible hazards and carry out appropriate corrective action to prevent injuries or damage arising from these hazards. Whether there is such a principle as due diligence concerning the treatment of aliens is uncertain. Nonetheless, it is sufficient that a State treat aliens according to international minimum standards. Regarding terrorism, due diligence is merely at issue when it comes to State tolerance of activities carried out against other States. In my opinion, due diligence could well function as the one and only fundamental principle within all these areas of international law because of its uncomplicated content: a minimum level of efforts which a State must undertake to fulfil its international responsibilities. However, the examination of these areas demonstrates that the concept of due diligence has a flexible character and its content is thus not uniform. The largest similarity between the various areas is that due diligence is solely at issue when it comes to the duty of protection. There are indications in State practice that the degree of effectiveness of the State's control over its territory, the importance of the interests to be protected and the predictability of harm are factors a State should consider before taking action. A significant difference emerges concerning the various levels of strictness in the behaviour of a State. Often it is enough if a State behaves according to the standard of due diligence, but sometimes the State needs to follow a stricter standard, or even an absolute one. Due diligence can also be measured by technical and scientific standards of behaviour, for example regarding polluting industrial activities. In conclusion, obligations with a precise content can reduce the general and flexible nature of due diligence.