A new American Girl doll is released every year as part of the "Girl of the Year" collection. This is done to keep the dolls in line with current trends. American Girl's historical doll line, "BeForever," does not release new dolls on a set schedule.
American Girl's other doll lines, "My American Girl" and "Bitty Baby," do not release new dolls. Both of these lines are fully customizable at the time of purchase; there is no need to create new doll designs.
"Girl of the Year" dolls are retired on a set schedule; the prior year's doll is retired when the current doll goes up for sale. "BeForever" historical dolls are periodically retired and replaced with new dolls, but this does not happen on a regular schedule.