The tech tree in Civilization IV is very flexible, thanks to the addition of OR gates and the elimination of static eras. It's now possible to reach certain technology by researching different techs. For example, you can get to Gunpowder by researching either Guilds or Education. There is also no longer a minimum number of turns needed to discover a technology, making it easier to come back and get older technologies that you haven't researched yet. In addition, Great People can be used to help with research. Each great people type can usually research a certain type of techs. For example, a Great Prophet can help research a religion tech, while a Great Artist can help research a cultural tech.

NOTE: Information in this section is correct as of Civ4 v1.61.

Below are the detailed info for all 86 technologies in Civilization IV:

Icon	Technology	Cost	Requires	Leads To	Units Enabled	Buildings Enabled	Special Abilities
	Agriculture	60		Pottery, Animal Husbandry			Can build Farms
	Alphabet	300	Writing	Literature (with Polytheism), Drama			Enables tech trading
	Animal Husbandry	100	Agriculture or Hunting	Writing, Horseback Riding			Reveals Horse Can build Pastures
	Archery	60	Hunting		Archer, Skirmisher, Longbowman, Crossbowman, Cho-Ko-Nu, Horse Archer, Keshik, Camel Archer
	Artillery	4000	Physics, Steel, & Rifling	Rocketry	Artillery
	Assembly Line	5000	Corporation & Steam Power	Fascism (with Nationalism), Industrialism (with Electricity)	Infantry	Factory Coal Plant Pentagon
	Astronomy	2000	Calendar & Optics	Scientific Method (with Printing Press), Physics (with Scientific Method)	Galleon Frigate	Observatory	Obsoletes Colossus Enables trade on Ocean
	Banking	700	Currency & Guilds	Economics (with Education), Replacement Parts (with Printing Press)		Bank	Enables mercantilism
	Biology	3600	Chemistry & Scientific Method	Medicine (with Optics), Ecology (with Plastic or Fission), Refrigeration (with Electricity)			Can build farms w/o irrigation Farm produces +1 food
	Bronze Working	120	Mining	Iron Working, Metal Casting (with Pottery)	Axeman		Reveals Copper Enables Slavery Can chop down forests
	Calendar	350	Sailing & Mathematics	Astronomy (with Optics)			Can build Plantations Centers world map Obsoletes Stonehenge & Obelisk
	Chemistry	1800	Engineering & Gunpowder	Scientific Method (with Printing Press), Biology (with Scientific Method), Steam Power (Replaceable Parts), Steel (with Iron Working)	Grenadier, Frigate		Workshops +1 production, Obsoletes Parthenon
	Civil Service	800	Code of Laws or Feudalism	Paper, Nationalism (with Divine Right or Philosophy)	Maceman, Samurai		Farms spread irrigation Enables Bureaucracy
	Code of Laws	350	Writing & (Priesthood or Currency)	Civil Service, Philosophy (with Meditation), Constitution (with Nationalism)		Courthouse Chichen Itza	First to discover founds Confucianism. Enables Caste System
	Combustion	3600	Railroad	Flight (with Physics), Plastics (with Industrialism)	Transport, Destroyer, Submarine		Can build oil wells. Obsoletes whale
	Communism	2800	Liberalism & Scientific Method		Spy	Scotland Yard Kremlin	Enables permanent alliances, Enables State Property
	Compass	400	Sailing & Iron Working	Optics (with Machinery)	Explorer	Harbor
	Composites	7500	Plastics & Satellites	Future Tech (with Genetic)	Modern Armor, Jet Fighter, Stealth Bomber
	Computers	6500	Radio	Genetics (with Refrigeration), Fiber Optics (with Plastics or Satellites), Robotics (with Plastics)	Modern Armor	Laboratory	Obsoletes Angkor Wat & Spiral Minaret
	Constitution	2000	Code of Laws & Nationalism	Democracy (with Printing Press), Corporation (with Economics)		Jail	Enables Representation
	Construction	350	Masonry & Mathematics	Engineering (with Machinery)	War Elephant, Catapult	Colosseum	Enables bridge building
	Corporation	1600	Constitution & Economics	Assembly Line (with Steam Power)		Wall Street	Obsoletes Great Lighthouse +1 trade route per city
	Currency	400	Mathematics	Code of Laws (with Writing), Banking (with Guilds)		Market Grocer	Enables gold trading via diplomacy. +1 trade route per city
	Democracy	2800	Constitution & Printing Press			Statue of Liberty	Enables Universal Suffrage & Emancipation
	Divine Right	1200	Theology & Monarchy	Nationalism (with Civil Service)		Versailles Spiral Minaret	First to discover founds Islam
	Drama	300	Alphabet	Music (with Mathematics), Philosophy (with Meditation)		Theater Globe Theater	Can adjust culture rate
	Ecology	5500	Biology & (Plastics or Fission)			Recycling Center SS Life Support	Can scrub Fallout
	Economics	1400	Banking & Education	Corporation (with Constitution)			First to discover receives a Great Merchant. Enables Free Market Obsoletes Castle
	Education	1800	Paper	Liberalism (with Philosophy), Economics (with Banking), Gunpowder		University Oxford University
	Electricity	4500	Physics	Fission, Industrialism (with Assembly Line), Refrigeration (with Biology), Radio		Bunker Bomb Shelter Broadway	Windmills: +1 commerce Watermills: +2 commerce
	Engineering	1000	Machinery & Construction	Chemistry (with Gunpowder)	Pikeman	Castle Hagia Sophia	+1 road movement
	Fascism	2400	Assembly Line & Nationalism			Mount Rushmore	Enables Police State Can negotiate permanent alliances
	Feudalism	700	Writing & Monarchy	Civil Service, Guilds (with Machinery)	Longbowman		Enables Vassalage, Serfdom
	Fiber Optics	7500	Computers & (Plastics or Satellites)	Fusion (with Fission)		The Internet SS Cockpit	Obsoletes Kremlin
	Fishing	40		Sailing, Pottery (with The Wheel)	Work Boat		Can work water tiles Can create Fishing Boats
	Fission	5500	Electricity	Ecology (with Biology), Fusion (with Fiber Optics)	ICBM	Nuclear Plant Manhattan Project
	Flight	5000	Physics & Combustion	Rocketry (with Rifling)	Carrier, Fighter, Bomber, Gunship, Jet Fighter, Stealth Bomber	Airport
	Fusion	8000	Fission & Fiber Optics			SS Engine	First to discover receives a Great Engineer
	Future Tech	10000	Composites & Genetics				+1 health & +1 happy face in all cities
	Genetics	7000	Computers & Refrigeration	Future Tech (with Composites)		SS Stasis Chamber	+3 health in all cities
	Guilds	1000	Feudalism & Machinery	Banking (with Currency), Gunpowder	Knight, Camel Archer, Conquistador	Grocer	Workshop: +1 Hammer
	Gunpowder	1200	Guilds or Education	Chemistry (with Engineering), Rifling (with Replaceable Parts)	Musketman, Musketeer, Cavalry, Cossack
	Horseback Riding	250	Animal Husbandry		Horse Archer, Keshik, Knight, Camel Archer, Conquistador, Cavalry, Cossack
	Hunting	40		Archery, Animal Husbandry	Scout, Spearman, Phalanx		Can build Camps
	Industrialism	6500	Electricity & Assembly Line	Plastics (with Combustion)	Marine, Navy SEAL, Tank, Panzer, Battleship		Reveals Aluminum Obsoletes Ivory
	Iron Working	200	Bronze Working	Compass (with Sailing), Steel (with Chemistry)	Swordsman, Jaguar, Praetorian		Reveals Iron Can remove Jungle
	Liberalism	1400	Philosophy & Education	Communism (with Scientific Method)			First to discover receives a free tech. Enables Free Speech & Free Religion
	Literature	200	Polytheism & Alphabet	Music (with Mathematics)		Heroic Epic National Epic Great Library
	Machinery	700	Metal Casting	Guilds (with Feudalism), Printing Press (with Paper), Engineering (with Construction), Optics (with Compass)	Crossbowman, Cho-Ko-Nu, Maceman, Samurai		Can build windmill & watermill
	Masonry	80	Mining or Mysticism	Monotheism (with Polytheism), Construction (with Mathematics)		City Walls Aqueduct Pyramids Great Lighthouse	Can build quarry
	Mass Media	3600	Radio			Broadcast Tower Hollywood United Nations
	Mathematics	250	Writing	Music (with Literature or Drama), Calendar (with Sailing), Construction (with Masonry), Currency		Aqueduct Hanging Gardens	Can build fort. Workers produces 50% more hammers from chopping
	Medicine	4500	Optics & Biology			Hospital Red Cross	Enables Environmentalism
	Meditation	80	Mysticism	Priesthood, Philosophy (with Code of Laws or Drama)		Monastery	First to discover founds Buddhism
	Metal Casting	450	Pottery & Bronze Working	Machinery		Forge Colossus	Can build workshop
	Military Tradition	2000	Music & Nationalism		Cavalry, Cossack	West Point	Enables defensive pacts
	Mining	50		Masonry, Bronze Working			Can build mines
	Monarchy	300	Priesthood or Monotheism	Feudalism (with Writing), Divine Right (with Theology)			Enables Hereditary Rule Can build wineries
	Monotheism	120	Masonry & Polytheism	Theology (with Writing), Monarchy			Enables Organized Religion First to discover founds Judaism
	Music	600	Mathematics & (Literature or Drama)	Military Tradition (with Nationalism)		Cathedral Notre Dame	First to discover receives a Great Artist
	Mysticism	50		Meditation, Polytheism, Masonry		Obelisk Stonehenge
	Nationalism	1800	Civil Service & (Philosophy or Divine Right)	Military Tradition (with Music), Constitution (with Code of Laws), Fascism (with Assembly Line)		Hermitage Taj Mahal	Enables Nationhood
	Optics	600	Compass & Machinery	Astronomy (with Calendar), Medicine (with Biology)	Caravel		+1 sight across water Can create whaling boats
	Paper	600	Theology or Civil Service	Education, Printing Press (with Machinery)			Enables map trading
	Philosophy	800	Meditation & (Drama or Code of Laws)	Nationalism (with Civil Service), Liberalism (with Education)		Angkor Wat	First to discover founds Taoism Enables Pacifism
	Physics	4000	Astronomy & Scientific Method	Electricity, Flight (with Combustion), Artillery (with Steel and Rifling)			Reveals Uranium First to discover receives a Great Scientist
	Plastics	7000	Combustion & Industrialism	Ecology (with Biology), Composites (with Satellites), Fiber Optics (with Computers), Robotics (with Computers)		Hydro Plant Three Gorges Dam	Obsoletes fur Can create Offshore Platform
	Polytheism	100	Mysticism	Priesthood, Monotheism (with Masonry), Literature (with Alphabet)		Parthenon	First to discover founds Hinduism
	Pottery	80	The Wheel & (Agriculture or Fishing)	Writing, Metal Casting (with Bronze Working)		Granary	Can build cottages
	Priesthood	60	Meditation or Polytheism	Monarchy, Code of Laws (with Writing), Writing		Temple Oracle	Can construct temple
	Printing Press	1600	Machinery & Paper	Democracy (with Constitution), Scientific Method (with Chemistry or Astronomy), Replaceable Parts (with Banking)			Villages & towns produce +1 commerce
	Radio	6000	Electricity	Mass Media, Computers, Satellites (with Rocketry)	Submarine, Bomber	Eiffel Tower Rock N Roll
	Railroad	4500	Steam Power & Steel	Combustion	Machine Gun		Can build railroads
	Refrigeration	4000	Biology & Electricity	Genetics (with Computers)		Supermarket	+1 extra move for water units
	Replaceable Parts	1800	Banking & Printing Press	Rifling (with Gunpowder), Steam Power (with Chemistry)			Can build lumbermills. Windmills & watermills +1 hammer
	Rifling	2400	Gunpowder & Replaceable Parts	Artillery (with Physics, Steel), Rocketry (with Flight or Artillery)	Rifleman, Redcoat, Infantry, Marine, Navy SEAL, Mech. Infantry, Tank, Panzer		Obsoletes Chichen Itza
	Robotics	8000	Plastics & Computers		Mech. Infantry, Stealth Bomber	SS Docking Bay Space Elevator
	Rocketry	5000	Rifling & (Flight or Artillery)	Satellites (with Radio)	SAM Infantry, Gunship, ICBM	SS Casing Apollo Program
	Sailing	100	Fishing	Calendar (with Mathematics), Compass (with Iron Working)	Galley	Lighthouse	Enables trade on coasts
	Satellites	6000	Radio & Rocketry	Composites (with Plastics), Fiber Optics (with Computers)		SDI SS Thrusters	Reveals world map
	Scientific Method	2400	Printing Press & (Chemistry or Astronomy)	Communism (with Liberalism), Physics (Astronomy), Biology (with Chemistry)			Reveals Oil Obsolete Great Library & Monastery
	Steam Power	3200	Chemistry & Replaceable Parts	Assembly Line (with Corporation), Railroad (with Steel)	Ironclad		Reveals Coal Workers build improvements +50% faster Obsoletes Hagia Sophia
	Steel	2800	Iron Working & Chemistry	Railroad (with Steam Power), Artillery (with Physics and Rifling)	Cannon, Ironclad	Drydock Ironworks
	The Wheel	60		Pottery (with Agriculture or Fishing)	Chariot, War Chariot, Immortal		Can build roads
	Theology	500	Writing & Monotheism	Divine Right (with Monarchy), Paper		Sistine Chapel	First to discover founds Christianity Enables Theocracy
	Writing	120	Priesthood or Animal Husbandry or Pottery	Code of Laws (with Priesthood or Currency), Feudalism (with Monarchy), Theology (with Monotheism), Mathematics, Alphabet		Library	Enables Open Borders

Related Links:

• The full Civ4 in-game tech tree
• More info about technologies are available in the Civilization IV Info Center.

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