Background: The concept of walkable neighborhoods is increasingly important in physical activity research and intervention. However, limited theoretical understanding and measurable definitions remain a challenge. Methods: This paper reviews theories defining neighborhoods and offers an empirical approach to identify measurable attributes and thresholds of walkable neighborhoods.  Bivariate and multivariate analyses are used for self-reported socio-demographic background, neighborhood walking behavior and perception, and objective measures of environments. Results: Environmental attributes positively associated with walking sufficiently to meet health recommendations included higher residential density and smaller street-blocks around home, and shorter distances to food and daily retail facilities from home. Threshold distances for eating/drinking establishments and grocery stores were 860 and 1445 feet. Conclusions: Results questioned theoretical constructs of neighborhoods centered on recreation and educational uses. They pointed to finer mixes of uses than those characterizing suburban neighborhoods, and small spatial units of analysis and intervention to capture and promote neighborhood walkability.