Dilemmas in a General Theory of Planning
Rittel, H.W.J. and M.M. Webber 1973. "Dilemmas in a General Theory of Planning." Policy Sciences 4 Amsterdam, The Netherlands: Elsevier Scientific Publishing Company, Inc.: 155–169. In Cross, N. 1984. Ed. "Developments in Design Methodology." Chichester, West Sussex, England, UK: John Wiley & Sons, Ltd. p. 135–144.
This source is considered a primary reference for the Socio-Technical Features of Systems of Systems article.
Horst Rittel and Melvin M. Webber formally described the concept of wicked problems in a 1973 treatise, contrasting "wicked" problems with relatively "tame," soluble problems in mathematics, chess, or puzzle solving ie the origin of the term ‘wicked problem.