As a city responds to its environment, it grows either outward, upward or both. This book focuses on underground construction as a response to urban development. The expanded fields of architecture now holds a new direction: down. Here we seek to review the steps needed in order to approach success when building below the surface. The relationship between a building and its surrounding environment usually defines the projects aesthetic and form, however, it is up to the architect to define the diastem between the final strata of the earth below and the urban infill of the sky above. Designing for such an alliance requires a greater understanding of the many aspects of subsurface urbanism.