In 1996, the magazine launched the Slate 60, a counterpoint to Forbes' annual list of the 400 wealthiest Americans. The idea came from Ted Turner, via Maureen Dowd of the New York Times. In an interview, the media mogul and philanthropist decried the state of modern giving, arguing that the crass annual ranking spurred big earners to hoard their wealth, to the detriment of society. "That list is destroying our country," Turner said. "That [list is] their Super Bowl."
The methodology for the list has evolved over the years, and the list is compiled based on "gifts and pledges to nonprofit organizations of cash, stock, land, art, and real estate." To explain further, gifts that philanthroprists make to foundations are counted, but not grants that those foundations make to deserving groups, to avoid double counting. For the same reason, we count pledges, but not payments on those pledges. Bequests are considered for the list, but are often listed in subsequent years after the estate has been settled or when more information is available about which groups will be receiving gifts. For more information, see this explantion from the Chronicle of Philanthropy.