<p>Previous studies have attempted to define segregation succinctly but have not reached a consensus. Adding to the unsettled debates was the shift from using place-based to person-based data in segregation studies. Deduced from the literature, the meanings of segregation may be summarized by the two essences of measuring the distribution of and interaction among different population groups, and measures may be characterized by four elements of segregation: dimensions, spatial extent, social extent, and data type. Besides showing a trend from using spatially aggregated place-based data to individual-level person-based data, a review of selected papers confirms the salience of distribution and interaction in measuring segregation and highlights the limitations of existing measures in capturing social interaction between population groups and the impacts of segregation, even in recent studies that utilize person-based data. Finally, we propose a segregation measurement framework to accommodate the increasingly hybrid physical-virtual world using person-based data with three components: <Emphasis Type="BoldItalic">distributions</Emphasis> of different groups, <Emphasis Type="BoldItalic">interactions</Emphasis> among groups, and <Emphasis Type="BoldItalic">inequality</Emphasis> experienced by different groups due to the disparities in accessing resources and opportunities. This review paper charts directions for future studies using segregation measures.</p>