Traditionally, the sources of international law are regarded as being listed in Article 38 of the Statute of the International Court of Justice.
- International Conventions whether general or particular establishing rules expressly recognized by 'the contesting states';
- International custom as evidence of a general practice accepted as law;
- The general principles of law recognised by civilised nations; and
- Judicial decisions and the teachings of the most highly qualified publicists of the various nations (as subsidiary means for the determination of rules of law).
Nowadays, the term ‘convention’ is assumed to be referring to a multilateral treaty; but at the time Article 38 of the UN Charter was drafted ‘convention’ denoted any sort of treaty: bilateral, plurilateral or multilateral. And in the context of Article 38 it still has this meaning.
Since WWII, treaties have assumed a clear prominence as the primary source of law-making on the international plane.
- Especially multilateral treaties.
- Even so, international tribunals have clarified customary international law in ways which have developed the legal principles governing the law applying to treaties. For example, the International Court of Justice has done a lot to clarify the general rules for the interpretation of treaties. 
- With the increased focus on relations between States that comes with globalisation, there has been greater pressure and demand to codify rules obtaining between those States.
- This codification has been done mainly through treaties because they are a relatively simple, clear and quick way of crystallizing existing international rules and developing new ones.
- Indeed, it is now commonplace for legal scholars to classify those treaties which lay down universal (or even fairly general) rules governing international society as 'law-making' or 'normative' treaties. The Hague Peace Conferences of 1898 and 1907 are often cited not only as a watershed in the institutionalisation of international co-operation, but also as the first major international ‘law-making’ conferences. 
So-called ‘normative treaties’ are:
- characterised metaphorically as 'international legislation', and
- extolled as necessary to accommodate the urgent dynamics that are transforming international relations.
Multilateral treaties – because they have a larger number of parties - are more effective than bilateral treaties in codifying international law.
- In negotiating multilateral treaties its parties often try to address the subject matter of the treaties as comprehensively as possible.
- Of course, States negotiating these agreements often have different or conflicting interests; so the final multilateral treaty text may not fully reflect the views and positions of all the States which negotiated it.
You can imagine how difficult it is to try and achieve conformity of views and approaches in relation to a multilateral instrument that is intended to be comprehensive – even where the instrument’s subject matter is relatively narrow.
Even if you can settle the text of a law-making treaty you then face the risk that it may conflict with other law-making treaties. And the legal principles for resolving these conflicts may prove – in particular cases – to be anything but clear and simple. 
There are many examples of law-making treaties.
A classic case is the Law of the Sea Convention, which took nearly a decade to negotiate.
- codifies the international law applying to the oceans and seas
- develops international law
- provides an invaluable source of the law relating to those aspects of the law of the sea which took its parties so long to negotiate, and
- is, by and large, extremely clear and explicit - even if there are some provisions that are ambiguous.
Another example of a codifying or 'normative' instrument is the Statute of the International Criminal Court (or ‘Rome Statute’).
The Rome Statute is regarded by some as the most important multilateral instrument negotiated in the last decade of the twentieth century.
- The Statute codifies international law regarding war crimes and other crimes against humanity.
- During the negotiation of the Statute momentum developed to create a comprehensive regime on such criminal law.
- This was premised on certain customary international law norms having achieved such broad acceptance internationally that they could be enshrined in a formal document which would be generally acceptable as binding to a large number of States.
The Statute illustrates how a treaty can not only crystallize putative customary international norms as conventional law, but also further develop such norms and related standards.
Of course, the outcomes of treaty negotiations are not always so exemplary. Negotiating States may refuse to adopt an international norm in a treaty because it does not suit their interests or because they sincerely believe that the norm does not represent customary international law.
In such cases you may get straightforward compromises; or you may get (what diplomats call) 'constructive ambiguity' where the meaning of the settled text is not clear.
This ambiguity allows the parties to interpret the treaty provisions in the way that most suits their interests. This may not sound like much of a solution, but often - with diplomats - 'half of something is better than a lot of nothing'. A 'fuzzy' treaty is better than none at all.
The Antarctic Treaty is an archetype of such a ‘treaty’ solution. During the 1950’s a ‘tacit agreement’ developed between certain states which were active in Antarctica. (It was called an ‘gentleman’s agreement’ in the sexist terminology of the times.) Under this agreement states would not try to advance or enhance claims to territorial sovereignty in Antarctica.
Arguably (although I would not want to argue this) the gentleman’s agreement constituted customary regional international law which was legally binding. However, it was not at all clear that the parties to this tacit agreement regarded their agreement as legally binding. Contrariwise, there had been many acrid territorial disputes over Antarctica, which the gentleman’s agreement had put a lid on. There was no optimism that this lid would stay on. And, if the lid blew off – with the parties terminating their tacit agreement – the consequences could have been quite grave. There were even fears of armed conflict between Argentina and the UK over their territorial disputes.
So, Article IV of the Antarctic Treaty addressed the problem by providing that: ‘No new claim, or enlargement of an existing claim, to territorial sovereignty in Antarctica …’ should be asserted while the Treaty was in force. This meant – in theory – that claims to Antarctica could neither be improved nor worsened. 
Article IV did not resolve the problem of competing claims to sovereignty in Antarctica. Indeed, it was depicted as the ‘non-solution of a problem that could never be swept completely under the carpet’.  However, the Treaty has undoubtedly promoted stability in the international politics of Antarctica. Moreover, what was originally regarded as a modus vivendi (that is an interim arrangement which stays in place till a legal solution is reached) now - with the passage of time - looks increasingly like it will bed down a permanent, legal status quo.
It is even being argued that the Antarctic Treaty has created an objective legal regime which is binding on all states irrespective of whether or not they are parties to the Treaty. (In much the same way as a bilateral treaty which changes borders between countries is regarded as objectively binding on all states.)
Just as interesting is the fact that a whole legal regime has sprung up from the fountainhead of Article IX of the Antarctic Treaty. This article provides that parties carrying out scientific research may - by consensus - recommend measures which further the objectives of the Antarctic Treaty. Article IX does not provide any measure adopted pursuant to it is legally binding; but the practice of the parties to the Antarctic Treaty shows that they normally regard such measures as legally binding. From 1961 to 1995 over 200 measures were promulgated under this provision regarding (among other things) environmental protection, telecommunications, tourism and mining.  A treaty that was once disdained as a ‘non-solution’ has proven to be the solid foundation for an exemplary international legal regime.
There was also criticism of the Antarctic treaty regarding the vagueness of its terms. For example, the term ‘territorial sovereignty’ is ambiguous. Lawyers could argue over whether claims to the territorial sea or the straight baselines adjacent to Antarctic territory are prohibited by Article IV of the Antarctic Treaty. Yet I prefer to see this terminology as reflecting 'constructive ambiguity'. This ambiguity is one of the reasons that the Antarctic Treaty has proved immensely useful in stabilising the international politics of Antarctica.
Sovereignty and Treaties
Finally, I come to an issue that continually arises - at least in the popular imagination - from treaties legally binding nature: treaties effect on national sovereignty.
A common refrain popularly espoused about treaties is that they surrender national sovereignty, and therefore represent a threat to Australia's national interest.
Ironically, the right to enter into a treaty - and to be legally bound by it - is a vital aspect of any nation's sovereignty. Without that right, a nation could not take its place in the civil society of nations.
So the place of Australian treaties is to serve the national interest by continually developing international law. The question we should be asking is not whether the treaty surrenders sovereignty; the real question we should be asking is whether - in entering into a treaty - enough consideration has been given to the rights and obligations and the costs and benefits arising from that treaty action.
The resounding answer to that question - as far as Australia is concerned is: yes - it has.
- Australia will not become Party to a treaty lightly.
- Australia's decisions to enter into treaties are only taken after widespread consultations and deliberations.
- These deliberations include scrutiny of treaty actions by the parliamentary Joint Standing Committee on Treaties aided by the institution of National Interest Analysis statements.
So treaties cannot now be depicted (like they were in the past) as being - in many cases - a convenient pretext which allows faceless bureaucrats to usurp Australia's sovereignty.
My essential point is that the twenty-first century is seeing an accelerating intermeshing of nations' actions and interests.
Consequently, treaties are an increasingly vital means of turning our interdependence with other nations to good - and better - advantage; of developing international law properly; and therefore - most importantly - of serving Australia's national interest.
1 GG Fitzmaurice, The Law and Procedure of the International Court of Justice: Treaty Interpretation and Other Treaty Points, 1951 BYBIL, pp 1-28; cf Article 31 Vienna Convention on the Law of Treaties, (23 May 1969).
2 IA Shearer, Starke's International Law, pp 37-39 (Cf P Reuter, Introduction to the Law of Treaties, p 26); J Hu, The Role of International Law in the Development of WTO Law, Journal of World Trade, 7 (1): pp 143-167, p 167, 2004.
3 C Wilfred Jenks, The Conflict of Law-making Treaties, 1953 BYBIL, pp 401-453; cf Joost Pauwelyn, How to Win a World Trade Organization Dispute Based on Non-World Trade Organization Law, Journal of World Trade, 37 (6): pp 997-1030, 2003.
4 PJ Beck, The International Politics of Antarctica, p 118.
5 PJ Beck, above, p 118.
6 A Aust, Modern Treaty Law and Practice, p. 97, p 209.