While the idea of the "American Dream" was first alluded to in the U.S. Declaration of Independence, the phrase "American Dream" first became popular through the writings of James Truslow Adams in his 1931 book "The Epic of America." In it, he defines what the American Dream means.
Although the phrase "American Dream" goes all the way back to the writings of Benjamin Franklin, it was Adams's usage that drew it into common usage. In "The Epic of America," Adams defined the American Dream as one of "a land in which life should be better and richer and fuller for everyone, with opportunity for each according to ability or achievement." He further specified that it was not a dream solely focused on material prosperity, though some people later interpreted it as such.