The recent beta launch of Mark Twain Project Online (MTPO) supersedes the catalog previously provided here in both up-to-date content and functionality. Within MTPO's Letters area one may now browse and read edited texts of letters Mark Twain wrote between 1853 and 1880, with annotation through 1876. MTPO also provides full search capabilities.

MTPO's letters catalog may be visited by choosing either of these links, which recall the old catalog's choices:

• Outgoing Letters: all known letters written by Samuel L. Clemens and members of his immediate family.
• Incoming Letters: all known letters written to Clemens and his family, plus thousands of letters written to and by his extended family and associates.

Although a freestanding source list is no longer provided, each letter's owning repository is visible in the letter's "details" popup on MTPO.

The letters catalog provides an index to the letters, searchable by date, addressee, place, etc. To read the texts of letters after 1880, you may consult the files at the Mark Twain Papers, where every letter listed in the catalog can be found, either as a holograph, photocopy, printed text, or paraphrase. All letters owned in 1977 by the Mark Twain Papers (CU-MARK) are available on microfilm, which may be borrowed through an Interlibrary Loan Service. Microfilms of all letters known in 2001 are available for purchase.

The superseded outgoing and incoming search pages, as well as their source list, are still available. Please note, however, that they were last updated in 2005 and will not be maintained.