Different definitions and tests of dyslexia can cause unfairness and make life difficult for people with dyslexia as well as for the professionals. In 2012, the Danish government decided to support the fight against dyslexia. The government issued a public tender for the development of "a standardized, electronically administered test of dyslexia for use […] from primary Grade 3 and up through all educational levels to 5-year university education." The present paper reports from the development of this National Dyslexia Test. The paper focuses on the definition of dyslexia and the composition, reliability, and validity of the test. Data from the development of the test demonstrate the psychometric properties of the test. Reliability was indicated by a high agreement between the two (computer-administered) measures that are part of the test. External convergent validity was indicated by a high agreement between test results and results from prior practice and by agreement between test results and reading comprehension of educational texts. The paper concludes with a discussion of the practical uses and potential issues with the test since its release in 2015.