Section 51(xxix) of the Australian Constitution

Section 51(xxix) of the Australian Constitution is a subsection of Section 51 of the Australian Constitution that gives the Commonwealth Parliament of Australia the right to legislate with respect to "external affairs".

In recent years, most attention has focused on the use of the power to pass legislation giving effect within Australia to its obligations under international treaties and conventions. In some cases, as with human rights or environmental protection, the activities regulated by treaty-implementing legislation have not been international in nature but rather located solely within Australia or even solely within a particular State.

In Australia, developments in international law have no direct effect for domestic purposes unless a deliberate law-making act by the proper law-making authority has "transformed" the international rule into a domestic rule.

According to Constitutional law academic Michael Coper, it is "not entirely clear what the founding fathers intended" by conferring upon the Commonwealth Parliament the right to legislate with respect to "external affairs". Section 51(xxix) was amended a number of times in the Constitutional Conventions that debated the draft Constitution in the 1890s. The draft Constitution adopted by the 1891 Sydney Convention allowed the Parliament to make laws with respect to "External affairs and Treaties". This wording carried through the 1897 Adelaide Convention but the New South Wales Legislative Council, when considering whether to ratify the draft, resolved to omit the words "and Treaties" on the basis that only the Imperial Parliament ought to enter treaties that bound Australia. The removal of the explicit reference to treaties was confirmed by the delegates to the 1897 Sydney Convention and the 1898 Melbourne Convention.

In 1901, Robert Garran and John Quick suggested that the external affairs power would "prove to be a great constitutional battle-ground." Some 86 years later, Coper remarked that their prediction "showed remarkable foresight".

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