This invited special issue of "Early Education and Development" presents research related to the Early Development Instrument (EDI; Janus & Offord, 2007), a community tool to assess children's school readiness at a population level. In this editorial introduction, we first sketch out recent trends in school readiness research that call for a contextual and whole-child assessment of school readiness. Then we provide an overview of the EDI, including a discussion of its purpose and development, as well as its large-scale international use as a community tool to monitor children's developmental outcomes at population levels. Finally, we introduce the special issue's articles, all of which present research findings from ongoing community research projects that employ the EDI to assess children's school readiness. These articles are grouped into the following thematic themes: (a) individual-level validity of the EDI, (b) school and neighborhood effects and population-level validity of the EDI, and (c) program implementation and evaluation using the EDI. (Contains 2 footnotes.)