Johann George Adam Forster, also known as Georg Forster (German: [ˈɡeːɔʁk ˈfɔʁstɐ]; 27 November 1754 – 10 January 1794), was a German geographer, naturalist, ethnologist, travel writer, journalist and revolutionary. At an early age, he accompanied his father, Johann Reinhold Forster, on several scientific expeditions, including James Cook's second voyage to the Pacific. His report of that journey, A Voyage Round the World, contributed significantly to the ethnology of the people of Polynesia and remains a respected work. As a result of the report, Forster, who was admitted to the Royal Society at the early age of twenty-two, came to be considered one of the founders of modern scientific travel literature.

After returning to continental Europe, Forster turned toward academia. He taught natural history at the Collegium Carolinum in the Ottoneum, Kassel (1778–84), and later at the Academy of Vilna (Vilnius University) (1784–87). In 1788, he became head librarian at the University of Mainz. Most of his scientific work during this time consisted of essays on botany and ethnology, but he also prefaced and translated many books about travel and exploration, including a German translation of Cook's diaries.

Forster was a central figure of the Enlightenment in Germany, and corresponded with most of its adherents, including his close friend Georg Christoph Lichtenberg. His ideas, travelogues and personality influenced Alexander von Humboldt, one of the great scientists of the 19th century who hailed Forster as the founder of both comparative ethnology (Völkerkunde) and regional geography (Länderkunde). When the French took control of Mainz in 1792, Forster played a leading role in the Mainz Republic, the earliest republican state in Germany. During July 1793 and while he was in Paris as a delegate of the young Mainz Republic, Prussian and Austrian coalition forces regained control of the city and Forster was declared an outlaw. Unable to return to Germany and separated from his friends and family, he died in Paris of illness in early 1794, not yet 40.

The standard author abbreviation G.Forst. is used to indicate this person as the author when citing a botanical name.

Georg Forster was born in Nassenhuben (now Mokry Dwór, Poland), a small village near Danzig, on 27 November 1754. Georg was the oldest of seven surviving children of Johann Reinhold Forster, a Reformed Protestant pastor and scholar, and his wife Justina Elisabeth, née Nicolai. From an early age, Georg was interested in the study of nature, and his father first learned natural history from the books of Carl Linnaeus and then taught his son biology as well as Latin, French, and religion. In 1765, Reinhold obtained a commission by the Russian government to inspect the recently founded colonies near Saratov on the Volga River, which were mostly settled by German colonists. Ten-year old Georg accompanied his father on the 4,000 km (2,500 mi) journey, which reached the Kalmyk Steppe and Lake Elton, and collected hundreds of specimens of plants, helping his father with naming and identification. From October 1765, he attended Saint Peter's School in St Petersburg, while his father prepared a report about the state of the colony. Reinhold's report was critical of the voivode of Saratov and of the conditions in the colony, and the Forsters left Russia without payment amidst quarrel with Grigory Orlov. After a sea journey from Kronstadt, during which Georg learned English and practiced Russian, they arrived in London on 4 October 1766. Twelve-year old Georg competently translated Lomonosov's history of Russia into English and continued it until the present, and the printed book was presented to the Society of Antiquaries on 21 May 1767. His father took up a teaching position at Warrington Academy in June 1767, succeeding Joseph Priestley, leaving Georg behind in London as apprentice with a London merchant until the rest of the family arrived in England in September 1767. In Warrington, Georg learned classics and religion from John Aikin, mathematics from John Holt and French and natural history from his father.

The Forsters moved back to London in 1770, where Reinhold Forster cultivated scientific contacts and became a member of the Royal Society in 1772. After the withdrawal of Joseph Banks, he was invited by the British Admiralty to join James Cook's second expedition to the Pacific (1772–75). Georg Forster joined his father in the expedition again and was appointed as a draughtsman to his father. Johann Reinhold Forster's task was to work on a scientific report of the journey's discoveries that was to be published after their return.

They embarked HMS Resolution on 13 July 1772, in Plymouth. The ship's route led first to the South Atlantic, then through the Indian Ocean and the Southern Ocean to the islands of Polynesia and finally around Cape Horn back to England, returning on 30 July 1775. During the three-year journey, the explorers visited New Zealand, the Tonga islands, New Caledonia, Tahiti, the Marquesas Islands and Easter Island. They went further south than anybody before them, almost discovering Antarctica. The journey conclusively disproved the Terra Australis Incognita theory, which claimed there was a big, habitable continent in the South.

Supervised by his father, Georg Forster first undertook studies of the zoology and botanics of the southern seas, mostly by drawing animals and plants. However, Georg also pursued his own interests, which led to completely independent explorations in comparative geography and ethnology. He quickly learned the languages of the Polynesian islands. His reports on the people of Polynesia are well regarded today, as they describe the inhabitants of the southern islands with empathy, sympathy and largely without Western or Christian bias.