A sketch of their history and instructions for constructing them are most conveniently found amongst Martin Gardner's articles. The original presentation [1] dating from December of 1956, introduced triangle based flexagons, attributing their development to a group of graduate students at Princeton University in the late 1930's. The article was reprinted in his first puzzle collection [2], which is still on sale.

His first *Scientific American* article was followed in May of 1958 by a presentation of similar objects based on squares [3], duly reprinted in a second puzzle collection [4], also currently available. A third offering, oriented more toward ``flexatubes'' than flexagons, appears in a still later collection [5].

A definitive treatment of flexagons can be found in the RIAS Technical Report [7] of 1962 prepared by Anthony Conrad and Daniel Hartline, two students from Towson High School (near Baltimore, Maryland). Conrad's shorter summary [6] still covers the essential elements. Practically the only article which delves into a mathematical analysis of flexagons rather than giving a simple description of one of them is the analysis published by C. O. Oakley and R. J. Wisner in *American Mathematical Monthly* in 1957 [8]. Beyond that there are a dozen or so articles scattered through mathematical and recreational publications.

Since the Technical Report was never formally published and RIAS itself has been changed, there are only a few copies in existence, two of which have been deposited in Marhematical Recreations collections^{1}, and one of which has been optically scanned and placed on our web page^{2}. By and large, secondary references seem to have been lost, but those items which did get published can still be found in back issues of the corresponding periodicals. There is also a summary of recent activity [9].