The first voyage of James Cook is a combined Royal Navy and Royal Society expedition to the south Pacific ocean aboard HMS Endeavour, from 1768 to 1771.

It is the first of three Pacific voyages of which Cook is the commander.

The aims of this first expedition are to observe the 1769 transit of Venus across the Sun (3–4 June of that year), and to seek evidence of the postulated Terra Australis Incognita or "unknown southern land".The voyage is commissioned by King George III and commanded by Lieutenant James Cook, a junior naval officer with skills in cartography and mathematics.

Departing from Plymouth in August 1768, the expedition crosses the Atlantic, rounds Cape Horn and reaches Tahiti in time to observe the transit of Venus.

Cook then sets sail into the largely uncharted ocean to the south, stopping at the Pacific islands of Huahine, Borabora and Raiatea, and unsuccessfully attempting to land at Rurutu.

In September 1769, the expedition reaches New Zealand, being the second Europeans to visit there, following its earlier discovery by Abel Tasman 127 years earlier.

Cook and his crew spend the following six months charting the New Zealand coast, before resuming their voyage westward across open sea.

In April 1770, they become the first Europeans to reach the east coast of Australia, making landfall on the shore of what is now known as Botany Bay.The expedition continues northward along the Australian coastline, narrowly avoiding shipwreck on the Great Barrier Reef.

In October 1770, the badly damaged Endeavour comes into the port of Batavia in the Dutch East Indies, her crew sworn to secrecy about the lands they had discovered.

They resume their journey on December 26, round the Cape of Good Hope on March 13, 1771, and reach the English port of Deal on July 12.

The voyage has lasted almost three years.The year following his return, Cook sets out on a second voyage of the Pacific, which lasts from 1772 to 1775.

His third and final voyage lasts from 1776 to 1779.On his first voyage, Cook demonstrates by circumnavigating New Zealand that it is not attached to a larger landmass to the south; and although by charting almost the entire eastern coastline of Australia he had shown it to be continental in size, the Terra Australis being sought is supposed to lie further to the south.

Despite this evidence to the contrary, Alexander Dalrymple and others of the Royal Society still believe that this massive southern continent should exist.