Thailand's Capital, Bangkok, is located within a metropolitan region which has been developing, up until now, in a monocentric fashion. For this reason it has been labeled as a typical ‘primate city'. Resulting transportation and urban planning challenges were identified by AS+P and future development possibilities were studied. The initiative ‘Bangkok 21', triggered by ITS Consultancy, GTZ - Gesell­schaft für technische Zusammenarbeit and Siemens will highlight ways in which Bangkok can play a leading role among the metropolises of the 21st century. Sustainable urban growth adheres to the same assumptions as the ‘transit-oriented city', such that dense urban sub-centers exist at public transportation nodes. The plans for the public transit network within the structured (monocentric) urban area support the development of these sub-centers. Within the polycentric metropolitan region, an adequate public transportation system fosters the development of satellite cities, which form a system of central locations connected to one another. The areal development is restricted through regional green belts.