The Black-Allan Line is the eastern "straight-edge" portion of the state border between the Australian states of New South Wales and Victoria. The line stretches north-west from Cape Howe on the Tasman Sea to Indi Springs, the headwaters of the Murray River. The Murray River then forms the remainder of the boundary between the two states until it reaches the South Australian border.
The line is named for Alexander Black and Alexander Allan, the men who, between 1870 and 1872, surveyed the line that delineated the two colonies.
The boundary of the Port Philip District of New South Wales was defined in the New South Wales Constitution Act, 1842 (UK) as "... the boundary of the district of Port Phillip on the north and north east shall be a straight line drawn from Cape How to the nearest source of the river Murray and thence the course of that river to the eastern boundary of the province of South Australia." The Australian Constitutions Act, 1850 (UK) which established the colony of Victoria, uses the same definition.