Bill and Melinda Gates are among the world's leading philanthropists. They co-founded the Bill & Melinda Gates foundation in 2000 and have made philanthropy their full-time focus. The majority of their giving has focused on improving the health and well-being of the world's poorest people. The Gates Foundation's tagline is: "All Lives Have Equal Value." . In 2010, the Gateses and Warren Buffett started the Giving Pledge, a campaign that encourages the wealthiest people in the world to give at least half of their wealth to philanthropic causes.