Together, Braungart and McDonough wrote the Hannover Principles
in 1991, a set of guidelines for sustainable design created for the 2000 World's Fair in Hannover, Germany.
The Ahwahnee and Hannover Principles
were drafted by members of the design community, and the Natural Step was developed by scientists in Sweden.
The Hannover Principles
, developed in 1992 by William McDonough and Michael Braungart for the EXPO 2000 World Exposition, were among the first to integrate comprehensively the fundamental ideas of sustainability with the built environment.