Since cities inevitably will continue to densify, it is important to understand what are the key principles that lead to livability and subsequently sustainability.  It is not a question about can urbanism be sustainable, instead since urbanism is inevitable the question becomes “what needs to change to make urbanism sustainable.”  Urban density plays a vital role in the health of some of the most inhabited cities. If cities fail and become matrixes of gridlock with poisoned air and economic segregation, then the planet will follow. In contrast, if they succeed in bringing the next generation into sustainability by living lightly on the land they will contribute to the global trend toward a healthy environment. What approach will they take, high-rise developments or human scale with rich urban fabric?