Bracketology is the process of predicting the field of college basketball participants in the NCAA Basketball Tournament, named as such because it is commonly used to fill in tournament brackets for the postseason. It incorporates some method of predicting what the NCAA Selection Committee will use as its Ratings Percentage Index in order to determine at-large (non-conference winning) teams to complete the field of 68 teams, and, to seed the field by ranking all teams from first through sixty-eighth. Bracketology also encompasses the process of predicting the winners of each of the brackets. In recent years the concept of bracketology has been applied to areas other than basketball.     
Joe Lunardi is credited with inventing the term bracketology. Lunardi had been editor and owner of the Blue Ribbon College Basketball Yearbook, a preseason guide roughly 400 pages long.   In 1995, Blue Ribbon added an 80-page postseason supplement which was released the night the brackets were announced. So that the release could be timely, Lunardi began predicting the selection committee's bracket.   On February 25, 1996, The Philadelphia Inquirer referred to Lunardi as a bracketologist, which is the first known instance the term was applied to a college basketball expert.   While Lunardi did not recall using the term before its use in the article, Inquirer writer Mike Jensen credits its origins to Lunardi.  Lunardi soon started the website Bracketology.net,  and ESPN began running his predictions in exchange for a link to his website.  
Using the NCAA basketball tournament selection process, the RPI, and the seeding and balancing process, a "bracketologist" places teams in the tournament in the various regions (most commonly East, West, Midwest, and South however sometimes the region names are changed to reflect the host cities). Some bracketologists go as far as placing teams in which "pods" they will play in the first and second rounds.  Generally, the lists also show the last four teams in and the first four teams out. However, these brackets change daily as conference tournaments continue and teams automatically qualify for the tournament.
A bracketologist's credibility is judged on how many teams he predicts correctly being in the tournament and the average difference between the bracketologist's projected seed and the actual seed assigned by the NCAA Selection Committee. The difference between projected matchups and the differences between the "pods" selected in the first and second rounds are less important.[ citation needed]
Various methods are used to predict the winners in a bracket. While some use math and statistics, others make selections based on team mascots or colors.   President Barack Obama became famous for his bracket predictions.  Since entering office, he has presented his projected winners annually on ESPN in a segment called Barack-etology.   However, in 2015 he was bested by his former political rival, Mitt Romney, who ranked in the top 0.1 percent of entrants in ESPN's 2015 Tournament Challenge, correctly predicting six "Elite Eight" teams, each "Final Four" team, and the championship game matchup, while also correctly predicting Duke would win the title. 
Bracketology as a discipline has spread beyond a focus on basketball, into other sports, as well as pop culture, history, nature, and other topics where a loose application of binary opposition may be profitable for study or enjoyment,   albeit without the label of "bracketology" itself.
This spread has been helped along by literary agent and writer Mark Reiter and sports journalist Richard Sandomir, who have edited two books on bracketology as applied to the world around them, most recently The Final Four of Everything,  which was published by Simon & Schuster in May 2009.
- Sorting It All Out... with Brackets : NPR
- Sandomir, Richard; Reiter, Mark (March 22, 2007). "Books -- 'The Enlightened Bracketologist'". The Washington Post.
- "Baracketology". The Washington Post. April 4, 2009.
- Reiter, Mark (April 3, 2009). "Mark Reiter -- The Real Baracketology". The Washington Post.
- The Tournament of Books at The Morning News
- Robinson, Tom (February 26, 2006). "One man's Bracketology can plant seeds of a rich spring". The Virginian-Pilot. Archived from the original on May 21, 2006.
- Dietz, Brian (January 21, 2006). "Ten questions for Joe Lunardi". The News-Gazette. Archived from the original on March 4, 2015.
- Zimmer, Ben (March 21, 2014). "Marching Madly Into Brackets". The Wall Street Journal. Archived from the original on March 4, 2015.
- Jensen, Mike (February 25, 1996). "Kittles A Factor In Ncaa Bracket If Villanova Crashes Without Its Suspended Star, Its Shot At A No. 1 Seeding Is Gone. Uconn Stands To Gain". The Philadelphia Inquirer. Archived from the original on March 4, 2015.
- Bracketology | Saint Joseph's University
- Columns - CBSSports.com
- "March Madness Bracketology: The Science". Discover.com. March 15, 2012. Archived from the original on March 3, 2015.
- Pells, Eddie (March 19, 2013). "Bracketology: March Madness Brackets Are Everywhere, Including Cincinnati Classroom". huffingtonpost.com. Associated Press. Archived from the original on March 3, 2015.
- Leitch, Will. "Presidential Bracketology". Sports On Earth. Major League Baseball. Archived from the original on March 3, 2015.
- Corasaniti, Nick (March 19, 2014). "Obama's Bracket: Michigan State vs. Louisville in Final". The New York Times. Archived from the original on March 3, 2015.
- Bialik, Carl (March 31, 2014). "President Obama's Brackets: Apolitical, Cautious And Full of Chalk". fivethirtyeight.com. Archived from the original on March 3, 2015.
- DeMartino, Joe (April 7, 2015). "Mitt Romney's March Madness bracket was astoundingly good". ESPN.
- "Archived copy". Archived from the original on 2009-04-24. Retrieved 2009-05-05.
- "Archived copy" (PDF). Archived from the original (PDF) on 2011-07-08. Retrieved 2009-05-05.
- The Final Four of Everything | Book by Mark Reiter, Richard Sandomir - Simon & Schuster
- Bracketology article in New York Times
- Publisher website for The Final Four of Everything by Mark Reiter and Richard Sandomir
- ESPN: Joe Lunardi's Men's Bracketology
- ESPN: Charlie Creme's Women's Bracketology
- DRatings: Donchess NCAA/NIT Bracketology
- Bracketeers website for miscellaneous voting brackets
- The Bracket Project