1. For an earlier, German-language collection of Schenker's diaries and letters, see Hellmut Federhofer, Heinrich Schenker: Nach Tagebüchern und Briefen in der Oswald Jonas Memorial Collection, University of California, Riverside (Hildesheim: Georg Olms, 1985).
2. The earliest document hosted on SDO is a letter from Schenker to Ludwig Bösendorfer of ca. 1889–90, requesting a better piano to aid in his “theoretical studies”: http://www.schenkerdocumentsonline.org/documents/correspondence/GdM-Briefe-HS_1.html (accessed July 25, 2015). The latest document is a postcard sent to Jeanette Schenker dated September 18, 1939: http://www.schenkerdocumentsonline.org/documents/correspondence/OJ-12-24_12.html (accessed July 25, 2015).
3. Detailed information about SDO's participants and history is available through following the “Project Information” tab on the site's main navigation bar.
4. “Project Aims,” accessed July 8, 2015, http://www.schenkerdocumentsonline.org/project_information/project_aims.html.
5. Books and dissertations include Heinrich Schenker: Selected Correspondence, ed. Ian Bent, David Bretherton, and William Drabkin (Woodbridge, UK: Boydell Press, 2014); Nicholas Marston, Heinrich Schenker and Beethoven's “Hammerklavier” Sonata, Royal Musical Association Monographs 23 (Farnham, UK: Ashgate, 2013); Georg Burgstaller, “Kritikerdämmerung: Heinrich Schenker and Music Journalism” (PhD diss., University of Southampton, 2015); and Kirstie Hewlett, “Heinrich Schenker and the Radio” (PhD diss., University of Southampton, 2014). Special journal issues include the Journal of Schenkerian Studies 4 (2010) and Music Analysis 34, no. 2 (July 2015). For a bibliography of other publications related to SDO, see section 6c(2) at http://www.schenkerdocumentsonline.org/colloquy/bibliography.html (accessed July 8, 2015).