The author is Professor at the Faculty for Spatial Planning, University of Dortmund. In the 1980s he developed the 'Theory and Concept of Action on Ecological Urban Restructuring" at the Wissenschafts-zentrum Berlin. Parallel to his research work he directed several model projects on ecological urban restructuring in Berlin and in other cities. The projects ranged from experimental eco-houses, pilot projects on the ecological restructuring of neighborhoods and urban districts, up to model projects on the ecological revitalization of urban-rural development. Besides the University of Dortmund he teaches as guest professor at the University of Aalborg, Denmark, and has received invitations for lectures and guest professorships at several other universities in various countries. Since 2001 he has been a member of the World Society of Ekistics (WSE). The text that follows is an expanded version of a paper presented at the WSE Symposion"Defining Success of the City in the 21st Century," Berlin, 24-28 October, 2001.