Bill Gates grew up in an upper middle-class family with two sisters: Kristianne, who is older, and Libby, who is younger. Their father, William H. Gates Sr., was a promising, if somewhat shy, law student when he met his future wife, Mary Maxwell. She was an athletic, outgoing student at the University of Washington, actively involved in student affairs and leadership. The Gates family atmosphere was warm and close, and all three children were encouraged to be competitive and strive for excellence. Bill showed early signs of competitiveness when he coordinated family athletic games at their summer house on Puget Sound. He also relished in playing board games (Risk was his favorite) and excelled at Monopoly.

Bill had a very close relationship with his mother, Mary, who after a brief career as a teacher devoted her time to helping raise the children and working on civic affairs and with charities. She also served on several corporate boards, including those of the First Interstate Bank in Seattle (founded by her grandfather), the United Way and International Business Machines (IBM). She would often take Bill along when she volunteered in schools and at community organizations.