The couple announced their separation in an e-mail to friends.
"This is very much a mutual and mutually supportive decision that we have made together following a process of long and careful consideration. We ask for respect for our privacy and that of our family, and we do not intend to comment further."
The Gores, who were married on May 19, 1970, at the National Cathedral in Washington, crafted an image as a happily married couple during his eight-year stint as vice president in the 1990s and a presidential candidate in 2000. The couple famously exchanged a long kiss during the 2000 Democratic presidential convention.
The Gores were telling friends they "grew apart" after 40 years of marriage and there was no affair involved, according to two longtime close associates and family friends, who spoke on the condition of anonymity because it was a personal matter.
According to the Associated Press, the associates said the Gores, over time, had carved out separate lives, with the former vice president on the road frequently. One of the associates said: "Their lives had gotten more and more separated."
Experts say it is not that uncommon.
"Sometimes you have to realize that the person you picked 40 years ago may not be the person you would pick today, based on how you evolved and grown up as an adult," said therapist Leslie Seppini.
Al Gore has been the head of the television network Current TV since its inception back in 2005. He has long been an environmental advocate. He won an Oscar for the documentary "An Inconvenient Truth."
The Gores have four adult children, Karenna, Kristin, Sarah and Albert III.
A spokesperson says that the decision to divorce is something they both wanted.
Eyewitness News reporter Lisa Hernandez contributed to this report.