According to the Congress for New Urbanism:
New Urbanism is a planning and development approach based on the principles of how cities and towns had been built for the last several centuries: walkable blocks and streets, housing and shopping in close proximity, and accessible public spaces. In other words: New Urbanism focuses on human-scaled urban design.
The principles, articulated in the Charter of the New Urbanism, were developed to offer alternatives to the sprawling, single-use, low-density patterns typical of post-WWII development, which have been shown to inflict negative economic, health, and environmental impacts on communities.