G4 or G-4 may refer to:

• G4 nations, four major nations seeking seats on the UN Security Council: Germany, Brazil, Japan, and India
• G4 bloc, the core leadership of the larger G20 trade bloc within the World Trade Organization (China, India, Brazil, and South Africa)
• Group 4 of the periodic table
• PowerPC G4, a type of microprocessor used by Apple Computer
• Power Mac G4, a series of personal computers made by Apple
• G4 (TV channel), a male-oriented (formerly video game oriented) TV channel
• G4 (band), a pop group on the ITV television programme The X Factor
• Allegiant Air (IATA code "G4")
• G4 star, a subclass of G-class stars
• Gulfstream G400 and G450, private jets
• Santa Clara County Route G4, a county highway in Santa Clara County, California, USA
• G4 (Hong Kong), a former VIP unit of the Hong Kong Police Force
• AEG G.IV, a German World War I heavy bomber

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