"People who write about spring training not being necessary have never tried to throw a baseball." - Sandy Koufax
Spring training is a period of time from mid-February to the late March or early April when players get in shape for the season. Currently, all 30 major league teams either train in Florida (the Grapefruit League) or Arizona (the Cactus League). World War II travel restrictions led to teams training very close to home with the Boston Red Sox using Medford, MA, Indiana and Maryland were also popular training spots for teams during the war years. After the end of World War II, spring training locations were spread out across the southern half of the country, with towns such as San Antonio, TX and Hot Springs, AR, being popular venues.
During spring training, young players get to prove themselves worthy for the major leagues and many veterans choose to retire rather than take a demotion to the bench or AAA. It is considered a time of hope as every team has a chance of a good season during spring training.
Beginning of Spring Training
Spring training traces its origins back to 1886. The "birthplace" of Spring Training baseball was Hot Springs, AR, the city that first welcomed a major league team before the start of the regular season. The Chicago White Stockings (now the Chicago Cubs) first brought their coaches and players to the city that year in preparation for the upcoming season. Team President Albert Spalding (owner of Spalding Sporting Goods) and the team's player/manager Cap Anson, thought the city was an ideal training site for the players and wanted them to be in shape following a winter of baseball inactivity. The spas, accommodations and available fields in Hot Springs were a draw. The first known baseball location was the Hot Springs Baseball Grounds. After 1886, many other Major League teams soon adopted the philosophy and began training in Hot Springs. Needing venues for teams to use, Whittington Park was built in 1894, followed by Majestic Park (1908) and Fogel Field (1912). Overall, 134 members of the Hall of Fame are documented to have trained or played, in Hot Springs during early spring training. Eventually, better climates in Arizona, California and Florida drew teams from the Hot Springs locations. 
Current Spring Training Sites
Florida (Grapefruit League)
- Atlanta Braves - Champion Stadium - Lake Buena Vista, FL
- Boston Red Sox - JetBlue Park - Fort Myers, FL
- Baltimore Orioles - Ed Smith Stadium - Sarasota, FL
- Detroit Tigers - Joker Marchant Stadium - Lakeland, FL
- Houston Astros - Ballpark of the Palm Beaches - West Palm Beach, FL
- Miami Marlins - Roger Dean Stadium - Jupiter, FL
- Minnesota Twins - Hammond Stadium - Fort Myers, FL
- New York Mets - First Data Field - Port St. Lucie, FL
- New York Yankees - Steinbrenner Field - Tampa, FL
- Philadelphia Phillies - Bright House Networks Field - Clearwater, FL
- Pittsburgh Pirates - LECOM Park - Bradenton, FL
- St. Louis Cardinals - Roger Dean Stadium - Jupiter, FL
- Tampa Bay Rays - Charlotte Sports Park - Port Charlotte, FL
- Toronto Blue Jays - Florida Auto Exchange Stadium - Dunedin, FL
- Washington Nationals - Ballpark of the Palm Beaches - West Palm Beach, FL
Arizona (Cactus League)
- Arizona Diamondbacks - Salt River Fields at Talking Stick - Salt River Pima-Maricopa Indian Community
- Chicago Cubs - Sloan Park - Mesa, AZ
- Chicago White Sox - Camelback Ranch - Glendale, AZ
- Cincinnati Reds - Goodyear Ballpark - Goodyear, AZ
- Cleveland Indians - Goodyear Ballpark - Goodyear, AZ
- Colorado Rockies - Salt River Fields at Talking Stick - Salt River Pima-Maricopa Indian Community
- Kansas City Royals - Surprise Stadium - Surprise, AZ
- Los Angeles Angels of Anaheim - Tempe Diablo Stadium - Tempe, AZ
- Los Angeles Dodgers - Camelback Ranch - Glendale, AZ
- Milwaukee Brewers - Maryvale Baseball Park - Phoenix, AZ
- Oakland Athletics - HoHoKam Stadium - Mesa, AZ
- San Diego Padres - Peoria Sports Complex - Peoria, AZ
- San Francisco Giants - Scottsdale Stadium - Scottsdale, AZ
- Seattle Mariners - Peoria Sports Complex - Peoria, AZ
- Texas Rangers - Surprise Stadium - Surprise, AZ
- Thomas Boswell: "The Season of Sweet Boredom", in How Life Imitates the World Series, Penguin Books, New York, 1982, pp. 44-49.
- Anthony Castrovince: "Say Ball! The top cliches in camp are...", mlb.com, February 24, 2016. 
- Charles Fountain: Under the March Sun: The Story of Spring Training, Oxford University Press, New York, NY, 2009. ISBN 9780195372038
- Frank Jackson: "Crossing Red River: Spring Training in Texas", in The National Pastime - A Review of Baseball History, Society for American Baseball Research, Cleveland, OH, number 26 (May, 2006), pp. 85-91.
- Josh Pahigian: Spring Training Handbook: A Comprehensive Guide to the Ballparks of the Grapefruit and Cactus Leagues, McFarland, Jefferson, NC, 2013 (originally published in 2005). ISBN 978-0-7864-7195-9
- William F. Ross III: "Spring Training in Georgia: the Yannigans Are Coming!", in Baseball in the Peach State, The National Pastime, SABR, Volume 40 (2010), pp. 115-122.
- Dan Shaughnessy and Stan Grossfeld: Spring Training: Baseball's Early Season, Houghton Mifflin Company, New York, NY, 2003. ISBN 978-0618213993
- Ozzie Sweet: The Boys of Spring: Iconic Images from the Grapefruit League 1948-2004, SportClassic Books, 2005.