In this chapter we chronicle the Educational Testing Service’s (ETS) development and advancement of the family of web-based analysis applications known collectively as the Data Explorer (DX). The DX provides for secure primary and secondary analysis of National and International large-scale educational assessment (LSA) data on a public Web platform. It greatly simplifies the computationally intensive analyses that use these large, complex assessment databases, and provides reporting capabilities in the forms of tables and graphics. This chapter further provides an overview of the underlying Data Explorer Technologies (DXT™) that drive the application and how they have been leveraged to develop and deploy other quality control, analysis, and reporting methodologies. Although this chapter is directed to a non-technical audience, there are occasional digressions into certain technical issues for the curious reader and to give an idea of the complexities of the design and operation of the system.