Deutsches Geschlechterbuch is a series published by C.A. Starke Verlag and consisting of compiled genealogies of bürgerlich (non-noble) German families. Although published in German, each volume follows a standard format that makes it relatively easy for the non-German speaker to navigate them if familiar with a few key words and abbreviations. Some volumes focus on families from specific regions. A good overview of this source is in Shirley J. Riemer’s The German Research Companion, 3rd Edition (call no. R 292.1 R556G).
The St. Louis County Library History & Genealogy Department has volumes 1-221 with a few gaps. Volumes 1-216 are digitized on CD-ROMs. A cumulative index of surnames on CD-ROM for volumes 1-216, as well as some print indexes are also available. Each volume also includes a surname index to that volume.
Guides to library holdings and using the digitized volumes on CD-ROM can be downloaded as PDFs from the following links.