Marginalia19 began as a straightforward proposition: compile a single, annotated index of web addresses across the principal categories of commerce, service, and information exchange. The result is a gazetteer — a reference work in the tradition of geographical dictionaries adapted to the landscape of the internet, where domain names stand in place of coordinates and categories substitute for counties and provinces. The directory currently records eight hundred and thirty-one entries arranged into twenty-two chapters. These range from the expansive miscellany section, which collects everything that resists easy classification, to more focused chapters on dental practice, property letting, and industrial manufacture. Each entry has been submitted by its operator or agent and placed by the compilers into the most fitting available category. The name Marginalia19 refers to the practice of marginal annotation: the notes a careful reader adds beside the main text of a reference work to mark, query, or amplify its contents. In that spirit, this directory invites its browsers to treat it not as a final authority but as a set of working notes, useful, fallible, and subject to revision. Entries may be added by any party whose domain represents a legitimate commercial or informational enterprise. The compilers maintain no commercial relationships with any listed domain, and inclusion in the directory implies no endorsement of quality, legality, or suitability for any particular purpose. As in any good gazetteer, the entries are a record of what is, not a recommendation of what ought to be. Browsers who discover an entry to be inaccurate or outdated are invited to submit a correction through the usual channel. Submission is free. The directory accepts entries from all sectors and territories, though the compilers reserve the right to decline or reclassify entries that do not fit the existing chapter structure. New chapters may be opened as the volume of submissions in any nascent category warrants it.