Thomas Sieverts & S.K.T. develop a range of sustainable, contextually well-researched architecture and urban design projects for a diverse range of private and public sector clients. Thomas Sieverts is also the author of Zwischenstadt (1997; first published in English in 2000 as Cities without Cities: An interpretation of the Zwischenstadt), a book which addresses the decentralization of the compact historical European city and examines the new form of urbanity which has spread across the world best summarised as the urbanised landscape or the landscaped city. Sieverts calls this the Zwischenstadt, or "in-between city", the space that exists between old historical city centres and the open countryside, a mix of the natural and man–made. In historical terms, the Zwischenstadt is a newcomer, an interim stage in the transition to an uncertain future.