In 1929 the neighborhood concept was published separately in two forms. First was the neighborhood idea of Clarence Stein and Henry Wright, exemplified in their plan for Radburn. Second was the Neighborhood Unit idea of Clarence Perry. Since then, for the past seven decades, the concept has been applied and adapted internationally. Over this period the concepts original principles of neighborhood physical design, in both its forms, have varied with little controversy. What has been and is still an issue is the nature of the relationship between the neighborhood's physical arrangement and the social interaction among its residents. The conceptual framework adopted for analysis of this issue is to consider three basic approaches to the physical-social relationship: the equivocal, opportunistic, and deterministic modes. These approaches comprise a physical design-social interaction continuum of the neighborhood concept. Applications of the concept in North America, Britain, and elsewhere are examined and identified with one of the three approaches on the design-interaction continuum. In addition, comparisons of the original concepts of Stein and Wright with those of Perry, and their applications, are briefly undertaken. After review of seventy years of studies it is concluded that when considering the relation between neighborhood physical arrangement and social interaction that residential design should focus on users at the micro-neighborhood scale using an opportunistic approach.