April 2013 - Past Presidents and the current President at the dedication of the George W. Bush Presidential Center. L-R: Jimmy Carter, Bill Clinton, George H. W. Bush, George W. Bush, and President Barack Obama.
Here Are All 5 Living Presidents Together at the George W. Bush Library
But the crown for most-gathered actually belongs to First Ladies. Here's a 1994 photograph of First Lady Hillary Clinton (far right) along with (from left) Lady Bird Johnson, Betty Ford, Rosalynn Carter, Nancy Reagan, and Barbara Bush.
President Barack Obama laughs with former Presidents Jimmy Carter, Bill Clinton, and George W. Bush, prior to the dedication of the George W. Bush Presidential Library and Museum on the campus of Southern Methodist University in Dallas, Texas, April 25, 2013. (Official White House Photo by Pete Souza)