With its 1.5 million words BLUR is the biggest electronic corpus of nonstandard English. The present study describes the stages in the design, the compilation, and the editing of BLUR and attempts to gauge its linguistic profit. This is done both from a theoretical perspective - blues poetry vs. natural speech, representativeness, validity - and from an analytical perspective in particular qualitative, quantitative, and comparative analyses of morphological, morphosyntactic, and syntactic features. The findings indicate that BLUR provides an outstandingly rich and reliable documentation of the vernaculars spoken by African Americans between the Civil War and World War II. The more than 1,000 illustrative examples presented throughout this study attest to the correctness of this statement. Contents: Earlier African American English: origins debate, data sets - The blues as linguistic data: history, documentation, representativeness, validity - The BLUR corpus: corpus linguistics; design, compilation, annotation of BLUR - Analysis: morphology, morphosyntax, syntax; qualitative, quantitative, comparative; core - marginal - neglected features - Further down the road: research arenas.