He wrote a series of books that helped popularize and develop understanding of recreational cross-country skiing in the United States.

Born in Detroit, Michigan,[3] Caldwell grew up in Somerset, Pennsylvania[1] and moved to Putney, Vermont with his parents in 1941.

[4] Caldwell and his wife, Hep (née Hester Goodenough),[5] had four children, Tim, Sverre, Peter, and Jennifer.

[6] His son, Sverre, is a noted cross-country ski coach[14] whose daughter, Sophie, finished sixth in the sprint freestyle event at the 2014 Winter Olympics in Sochi, Russia, the highest finish by a U.S. woman in Olympic cross-country skiing at that time.

[15] In addition to writing on cross-country skiing for magazines and on line, Caldwell was the author of the following books: