Although it has long been known that Beethoven began composing a piano trio in F minor in 1816, scholarly examination of the extant sources for this unfinished project has only recently progressed beyond Nottebohm's brief remarks in the 1880s. The present article reveals the existence of numerous new sources evidently unknown to Nottebohm, including a leaf which forms the continuation of the draft score (Concept) of the first movement, the principal source for the trio. (Transcriptions of this score, including the new continuation, and of a newly identified draft which preceded it, accompany the article.) The trio project is contextualized in relation to other compositions, in particular the String Quartet in F minor, op. 95, the ‘Archduke’ Trio and the Piano Sonata in A, op. 101, and an attempt is made to understand the failure of the trio project in relation to Beethoven's limited compositional activity at this much-discussed point in his career.