The Diagnostic Evaluation of Language Variation (DELV) project comprises three tests—the DELV Screening Test (Seymour, Roeper, and de Villiers, 2003a, 2018), the DELV-Criterion Referenced (Seymour, Roeper, and de Villiers2003b), and the DELV-Norm Referenced (Seymour, Roeper, and de Villiers, 2005, 2018). They are the first, and so far, the most comprehensive linguistically sophisticated and culturally fair standardized language assessments on the market. They allow all speakers of English, including speakers of the AAE variety, to demonstrate competence in fundamental language elements and processes, and they provide linguistically-appropriate markers of impairment. Thanks to the unique team and the diverse expertise that contributed to their design and implementation, they stand out as ground-breaking both scientifically and socially. In this paper, I reflect on the confluence of ideas and circumstances that brought the DELV team together and created the tests. I then survey the continuing legacy of the tests in the first decade after they were published. Without sacrificing their very practical goals, the development and implementation of the DELV tests was first and foremost a research endeavor which addressed issues in theoretical and applied linguistics in the service of social justice. Indeed, the DELV’s creation allowed more comprehensive coverage of existing research topics and extensions to new questions about typical and disordered acquisition of different varieties of English. Once published, the DELV tests became both a tool and a focus for further research in the associated disciplines of linguistics, psychology, and communication disorders.