Positive inter-store externalities, sometimes termed as demand externalities (Eppli and Benjamin 1994), are the positive effects generated from one or more tenant(s) to other tenant(s) without consent and compensation between the generator and receiver. In previous research, demand externalities were usually seen as the synonym of customer-spillover effects generated from anchor tenants (Gatzlaff, et al. 1994; Pashigian and Gould 1998). These demand externalities have been recognized as significant agglomeration economies that generate increased returns in shopping centres. However, agglomeration economies in shopping centres could be more than just the spillover of customer drawing power of the anchor tenants. Under a wider definition of positive inter-store externalities, these inter-store effects should have a broader content including compatibility and complementarity among tenants, enhancement of the shopping atmosphere and resulting sales efforts, shopper circulation and the public services and facilities provided by the shopping centre. These positive interactive effects are the sources generating increasing returns.