Section 51(xxxi) of the Australian Constitution

Section 51(xxxi) of the Constitution of Australia is a subsection of Section 51 of the Constitution of Australia providing that the Commonwealth has the power to make laws with respect to "the acquisition of property on just terms from any State or person for any purpose in respect of which the Parliament has power to make laws." It is both a power and a constitutional guarantee of just compensation for property rights contingent on its exercise.

The provision states:

51. The Parliament shall, subject to this Constitution, have power to make laws for the peace, order, and good government of the Commonwealth with respect to:

The language of s 51(xxxi) was adapted from the final words of the Fifth Amendment to the United States Constitution. Unlike the American provision, however, it is primarily a grant of Commonwealth law-making power. It is clear that the requirement of "just terms" does not affect the State Parliaments. In Grace Bros Pty Ltd v The Commonwealth (1946) Justice Dixon stated that the inclusion of the condition was to "prevent arbitrary exercises of the power at the expense of a State or a subject."

The interpretation of the terms "acquisition" and "just terms" by the High Court of Australia have had the effect, however, of limiting its protection of property rights. Moreover, it operates at any time the Commonwealth makes a compulsory acquisition of property. As such, it is a contingent guarantee rather than a general constitutional right or freedom to enjoy property rights.

The Commonwealth may only acquire property on just terms for a "purpose in respect of which the Parliament has power to make laws". This means that every law supported by s 51(xxxi) must also be supported by at least one additional legislative power.

The effect of the section was the subject of the Australian film The Castle.

The High Court of Australia has taken a wide view of the concept of "property". Several members of the court took the opportunity to consider the meaning of the term property in Minister of State for the Army v Dalziel (1944). Justice Starke said the term includes: "every species of valuable right and interest including real and personal property, incorporeal hereditaments such as rents and services, rights-of-way, rights of profit or use in land of another, and choses in action. Justice McTiernan confirmed the term property extends to tangible and intangible property.

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