Unique / Luxury Resources give +5 happiness each. Try to scout early and find these, they are very valuable not only for the added happiness, but for trading with other civs for their own unique resources as well. Buildings that increase happiness:
Circus (if you have Iron and/or Horses nearby)
Colosseum
Courthouse (eliminates unhappiness from occupying a city)
Theatre
Stadium
The Burial Tomb, a unique building for the Egyptian civilization increases happiness as well.
Wonders that increase happiness:
Eiffel Tower
Notre Dame
The Hanging Gardens
Social Policies that increase happiness:
Legalism (Tradition)
Meritocracy (Liberty)
Military Caste (Honor)
Piety
Theocracy (Piety)
Cultural Diplomacy (Patronage)
Protectionism (Commerce)
Humanism (Rationalism)
Freedom
Planned Economy (Order)
Police State (Autocracy)
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