On his first voyage (1768-1771), he travelled to Tahiti to observe a transit of Venus, then explored the South Pacific for the mythical continent of Terra Australis. He reached New Zealand, which until then had been visited by Europeans only once (by Abel Tasman in 1644), and mapped its complete coastline, discovering Cook Strait which separates the North Island from the South Island. Next, he went on to Australia, discovered its east coast, and sailed through Torres Strait between Australia and New Guinea, again being only the second European to do so (the first being Luis Vaez de Torres, in 1604).
On Cook's second voyage (1772-1775), he laid the myth of Terra Australis to rest for good. He circumnavigated the globe at a very high southern latitude, became the first to cross the South Polar Circle, reaching 71°10' south, and discovered South Georgia and the South Sandwich Islands. During the southern winters, he made tours through the Pacific, and there discovered a number of islands as well.
On his last voyage (1776-1779), Cook explored the west coast of North America to look for a possible Northwest Passage. He discovered Hawaii, and explored the coast from California all the way to Bering Strait. On returning to Hawaii, he was killed in a fight with the local population.