The stamps feature the great hitter and Red Sox player Ted Williams, the Pirates' Willie Stargell, the Yankee Clipper Joe DiMaggio, and the Cleveland Indians' Larry Doby.
"Each of them represents not just a piece of baseball history but also of American history. Especially when you're looking at a guy like Larry Doby, the first African American to play in the American league, and the second African American to manage a team here for the Chicago White Sox in 1978," said Mark Reynolds, US Postal Service spokesperson.
Supporters hope the stamps will help children learn about the historical athletes.
"Kids get mail out of the mailbox. So when they get mail out of the mailbox they can see the people on the stamps and they can learn from there. It spikes an interest," said Cynthia Ferrell, a little league coach.
The back of the stamp booklet features short biographies of the four baseball greats, including Stargell, who was famous for his towering home runs and sense of humor.
Former White Sox player Carlos May knew him well.
"Great guy and great kidder too. He'd hit the ball to left field and I said why don't you pull the ball? He said there's money to be made over there too. He was a good guy," said May.
The Forever Stamps are non-denominational first class postage, which means that they can be used to mail first class letters no matter what the postal rate.