This understatement by the International Law Commission will come as no surprise to any lawyer, domestic or international. It is especially true for treaties, which are the product of negotiations leading to compromises to reconcile, often wide, differences. For multilateral treaties, the greater the number of negotiating states, the greater is the need for imaginative and subtle drafting to satisfy competing interests and concerns. The process inevitably produces some wording that is unclear or ambiguous. Despite the care lavished on drafting, and accumulated experience, there is no treaty which cannot raise some question of interpretation. Most disputes submitted to international adjudication involve some problem of treaty interpretation. Just as construing legislation is the constant concern of the domestic practitioner, treaty interpretation forms a significant part of the day-to-day work of a foreign ministry legal adviser.

But it would be wrong to think also that only international courts and tribunals interpret treaties. Increasingly domestic courts are faced with issues that involve their interpretation. For many years, one of the most common has been the meaning of ‘accident’ in the Warsaw Convention 1929, and its successive treaties. Most recently, courts in different jurisdictions have had to determine whether contracting deep vein thrombosis (DVT) during a flight was an accident.

A small, but nevertheless troublesome, example of a practical interpretation problem is to be found in the Comprehensive Nuclear-Test-Ban Treaty 1996 (CTBT).