Gates studied the work of Andrew Carnegie and John D. Rockefeller, and donated some of his Microsoft stock in 1994 to create the "William H. Gates Foundation." In 2000, Gates and his wife combined three family foundations and Gates donated stock valued at $5 billion to create the charitable Bill & Melinda Gates Foundation, which was identified by the Funds for NGOs company in 2013, as the world's wealthiest charitable foundation, with assets reportedly valued at more than $34.6 billion. The foundation allows benefactors to access information that shows how its money is being spent, unlike other major charitable organizations such as the Wellcome Trust. Gates, through his foundation, also donated $20 million to Carnegie Mellon University for a new building to be named Gates Center for Computer Science which opened in 2009.
Gates married Melinda French on a golf course on the Hawaiian island of Lanai on January 1, 1994. They have three children. The family's residence is an earth-sheltered mansion in the side of a hill overlooking Lake Washington in Medina, Washington. In 2009, property taxes on the mansion were reported to be US$1.063 million, on a total assessed value of US$147.5 million. The 66,000-square-foot (6,100 m) estate has a 60-foot (18 m) swimming pool with an underwater music system, as well as a 2,500-square-foot (230 m) gym and a 1,000-square-foot (93 m) dining room.
Gates purchased the Codex Leicester, a collection of scientific writings by Leonardo da Vinci, for US$30.8 million at an auction in 1994. Gates is an avid reader, and the ceiling of his large home library is engraved with a quotation from The Great Gatsby. He also enjoys playing bridge, tennis, and golf. Gates's days are planned for him on a minute-by-minute basis, similar to the U.S. President's schedule. Despite his wealth and extensive business travel, Gates flew coach in commercial aircraft until 1997, when he bought a private jet.