W3 or W-3 may refer to:

W3 (tram), a class of electric trams built by the Melbourne & Metropolitan Tramways Board

W3, a postcode district in the W postcode area

Apple W3, a wireless chip used in the Apple Watch Series 4.

PZL W-3 Sokół, a Polish helicopter

The Amazing 3, a manga and anime series, known in Japan as Wonder 3

Arik Air, which has IATA code W3

The fourth step of the W0-W6 scale for the classification of meteorites by weathering

The U.S. Internal Revenue Service form W-3, a transmittal form for Form W-2 information

Webster's Third New International Dictionary, the 1961 edition of Webster's Dictionary

The World Wide Web, abbreviated 'W3' on the earliest web pages

World Wide Web Consortium, international standards organization for the World Wide Web (abbreviated WWW or W3)

Windows 3.0, a Microsoft operating system