One of baseball's minor leagues, the Pioneer League is a Rookie Advanced League (just under single-A). Being a rookie league, no more than three players over the age of 23 can be on a team, nor can any player with more than three years of service. The league plays a split schedule of 76 games, with the first half winners playing the second half winners in a best-of-three series, the winners of the series playing each other in another best-of-three to determine the league champion.

The Pioneer League was founded in 1939, with the Boise Pilots, Lewiston Indians, Pocatello Cardinals, Twin Falls Cowboys, Ogden Reds and Salt Lake City Bees as the founding teams. Minor leagues being what they are, leagues expand, contract, move, and change quite rapidly - by 1964, when the Pioneer League became a short-season rookie league, there were only four teams - and of the original six, only Pocatello remained.

The ever changing Pioneer League has had teams in Montana (Billings, Butte, Great Falls, Helena, and Missoula), Idaho (Boise, Caldwell, Idaho Falls, Lewiston, Pocatello, and Twin Falls), Utah (Ogden, Provo, and Salt Lake City), and Alberta, Canada (Calgary, Lehtbridge, and Medicine Hat). The league's current configuration:

The Pioneer League has been home to many solid major leaguers, including Gary Sheffield, Steve Garvey, Andre Dawson, Pedro Martinez, and Jim Kaat.