A Voyage to Terra Australis: Undertaken for the Purpose of Completing the Discovery of that Vast Country, and Prosecuted in the Years 1801, 1802, and 1803, in His Majesty’s Ship the Investigator was a sea voyage journal written by English mariner and explorer Matthew Flinders. It describes his circumnavigation of the Australian continent in the early years of the 19th century, and his imprisonment by the French on the island of Mauritius from 1804–1810.

The book told in great detail of his explorations and included maps and drawings of the profiles of unknown coastline areas of what Flinders took to be as “Terra Australis Incognita”. By this, he was referring to the great unknown Southern continent that had been sighted and partly mapped by prominent earlier mariners such as Captain James Cook. The ship Flinders commanded, HMS Investigator, was a 334-ton sloop. Up until this time the circumnavigation of Australia which was necessary to prove it was a single continent land mass, had never been completed. He achieved this by circling the island continent, leaving Sydney in July 1801, heading north, through Torres Strait, across the top of the continent westward, and south along the western coastline. Flinders reached and named Cape Leeuwin on 6 December 1802, and proceeded to make a survey along the southern coast of the Australian mainland, and then completing the journey, arrived back in Sydney in June 1803, despite the dangerous condition of his ship.