Sustainable design and urban planning is guided by several principles borrowed from biology or the natural environment. These include the concepts of: (1) connectedness; (2) renewability; (3) efficiency; (4) minimization of externalities or negative impacts; and (5) carrying-capacity. Urban planners and designers that are interested in achieving sustainable development and communities use a variety of new urban design and planning principles and techniques to help achieve these concepts or goals of sustainability. These include smart growth strategies, new urbanism designs, sustainable urban infrastructure, new green building codes and designs, and new strategies to bring the natural environment back into our urban man-made environment. Following is a discussion of some of these techniques, beginning with new technological and building-design techniques and ending with sustainable land-use management techniques.