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Part 1: From 1998 to 2008 (written before 2008):

I thank the many people who have contributed to this Encyclopedia, starting with four fellow midwesterners, Larry Evans, Douglas Hofstadter, Jack Wetzel, and Peter Yff.

Douglas Hofstadter found the two intriguing transcendental triangle centers which bear his name, indexed in ETC as X(359) and X(360). In 1999, he hosted a four-day meeting for triangle geometers at his Center for Research on Concepts and Cognition at Indiana University. Among those attending were Larry Evans, Jack Wetzel, and Peter Yff.

Over the years, four of us have spoken at Jack's celebrated Geometry Potpourri Seminar at the University of Illinois, and five of us spoke, also at UI in 1999, at an AMS Special Session on geometry. It was Jack who observed that "Triangle geometry has more miracles per square meter than any other area of mathematics."

Peter Yff has been discovering new geometric relationships within ABC for more than forty years. These include X(190) and many centers conceived in connection with isoscelizers - see the note just before X(503) in ETC.

Also attending Doug's meeting were John Rigby and Cyril Parry, Englishmen who began publishing in geometry many years ago. Their letters to me over the years have been most helpful.

A whole new generation of names in triangle geometry has emerged relatively recently, many in connection with the work of the renowned mathematician, John Conway. John was drawn to triangle geometry at an early age. He has a notebook dating from those years and has been adding to it ever since. We all await his book-in-progress, known as The Triangle Book.

In December 1999, Antreas Hatzipolakis founded the internet list Hyacinthos, devoted to triangle geometry. Among the most active correspondents have been Edward Brisse, John Conway, Nikolaos Dergiades, Jean-Pierre Ehrmann, Bernard Gibert, Darij Grinberg, Michel R. Guillerault, Antreas Hatzipolakis, Michael Keyton, Floor van Lamoen, Sergey Markelov, Peter J. C. Moses, Peter Scales, Steve Sigur, Milorad Stevanovic, and Paul Yiu. All have contributed in one way or another to ETC, as have Joe Goggins, Richard Guy, Mowaffaq Hajja, and Manol Iliev.

Some of those mentioned here have their own websites, accessible via the LINKS button at the top of ETC. I encourage you to visit their sites.

Finally, I thank Nancy Heim, Melia Aldridge, and Juanita Chappell for their hours of careful typing, proof-reading, and library assistance.

Part 2: From 2009 to 2022

During 2009-2022, ETC has grown "exponentially" - in the sense that the growth rate seems roughly proportional to the size of the site. I thank the following contributors:

Kadir Altintas (Turkey)
Telv Cohl (Taiwan)
Jean-Pierre Erhman (France)
Emmanuel José García (Dominican Republic)
Bernard Gibert (France)
Antreas Hatzipolakis (Greece)
Tran Quang Hung (Vietnam)
Randy Hutson (Texas)
Seiichi Kirikami (Japan)
Floor van Lamoen (Netherlands)
César Eliud Lozada (Venezuela)
Angel Montesdeoca (Spain)
Peter J. C. Moses (England)
Alexei Myakishev (Russia)
Dao Thanh Oai (Vietnam)
Ivan Pavlov (Bulgaria)
Stanley Rabinowitz (New Hampshire)
Dan Reznik (Brazil)
Kiminari Shinagawa (Japan)
Ercole Suppa (Italy)
Suren (India)
Paul Yiu (Florida)
Peter Yff (Illinois)

Finally, a special thanks to Mark Mitchell (Texas), for reformatting ETC during July and August, 2022.