William Nelson Joy (born November 8, 1954) is an American computer engineer.
He co-founded Sun Microsystems in 1982 along with Scott McNealy, Vinod Khosla, and Andy Bechtolsheim, and served as chief scientist at the company until 2003.
He played an integral role in the early development of BSD UNIX while a graduate student at Berkeley, and he is the original author of the vi text editor.
He also wrote the 2000 essay Why The Future Doesn't Need Us, in which he expressed deep concerns over the development of modern technologies.