For a list of works devoted to Conrad's life and works, see A Bibliography of Books, Pamphlets, and Broadsides about Joseph Conrad, compiled by John G. Peters, University of North Texas.
Much of the Conrad canon is available online (see Links); however, the accuracy and reliability of these texts is often questionable, and the scholar cannot often be assured of the edition used. Useful for searching words or phrases, these tend to have more limited appeal for serious textual purposes.
Various works by Conrad (including some volumes of the Heinemann Collected Edition), as well as early works of criticism (Curle's 1914 study) and selected other sources, including Garnett's edition of letters to Conrad, are available at the Internet Archive, whose usefulness belies its appearance. Also available through the site are several first editions and Notes on My Books. Various first editions are also available at the Open Library and GoogleBooks.
All volumes of Heinemann's Collected Edition (1920-21, 1926-27) are available as PDFs on the website of the Bodleian Library, Oxford. The call number is 256 d.307: The Works of Joseph Conrad.
Volumes 1-3 of the Catalogue of the Library of John Quinn (1923) is available in digital form at Hathi Trust.
In July 2013 and July 2014 the late Stanley Seeger’s Joseph Conrad Collection was auctioned by Sotheby’s. Thanks to the generosity of Sotheby’s, the two auction catalogues are available here: LINK.
Stephen Donovan's project puts all the original serial publications online at Conrad First: The Joseph Conrad Periodical Archive, an invaluable resource supported in part by The Joseph Conrad Society (UK).
A useful complement to these are the full volumes of The English Review at the Modernist Journals Project.
Gene M. Moore's A Descriptive Location Register of Joseph Conrad's Literary Manuscripts (updated March 2016 version) is available here for download. The original print version (Autumn 2002, 27.2) may be ordered as a back issue of The Conradian (see Publications page for details).
The major Conrad libraries are listed on the Links page of this website. Conrad's main French sources and materials in French related to his experience in the French-speaking world and in Africa can be accessed at the Bibliotheque Nationale's website: Gallica.
Textual scholars may find of interest The Virtual Typewriter Museum, which helps in identifying the various typewriters used by Conrad's amanuenses, and the "Tuan Jim" manuscript, the origin of Lord Jim. Thomas J. Wise's Bibliography of Conrad may also be of interest.
The Beinecke Rare Book and Manuscript Library at Yale University, in addition to its rich collection of Conrad photographs, has put online the whole of 'Heart of Darkness' and The Shadow-Line, as well as several short stories collected in Tales of Unrest.
Conrad's reading may be canvassed by a search on the UK Reading Experience Database.
The Harry Ransom Center, University of Texas at Austin, offers online access to Conradiana, including the Victory MS and the Chance TS.