This treatise creates a foundation for preparing a new edition of Piano Sonata in C-sharp Minor, op. posth. 80, by Pyotr Il'yich Tchaikovsky. Composed in 1865, the year Tchaikovsky graduated from the St. Petersburg Conservatory, the work was not published during the composer's lifetime, and was therefore never subjected to the necessary corrections and revisions that the composer might have undertaken to prepare the work for publication. The manuscript was discovered among the composer's papers following his death, and was published in 1901 by Peter Jurgenson (Moscow), and was edited to an unknown degree by Sergei Taneyev. Subsequent editions were the Moscow State Library Edition of 1902, the Muzyka edition of 1972 and the Könemann Musica Budapest edition of 1993. The treatise gives historical and musicological descriptions of each of the available editions along with a brief history of the work. The study also explores the circumstances of the manuscript's disappearance. The bulk of the treatise, however, is focused on changes that may be beneficial to completing a critical edition of the work, and explaining how certain editorial decisions were made. A portion of this document considers Tchaikovsky as a pianist. First-hand accounts by his classmates at the St. Petersburg Conservatory are given, and include recollections of Hermann Laroche. An exploration of Tchaikovsky's relationship with the piano and its repertoire is also included. The treatise includes a brief analysis of the sonata focusing on those works which might have inspired Tchaikovsky as he sought to create, according to S[ ______ ] Frolova, the first Russian piano sonata. Some of the works which Tchaikovsky may have considered useful models include Chopin's Sonata in B-flat Minor, op. 35, Rubinstein's Sonata in F Major, op. 41, Schumann's Kreisleriana, op. 16, and Symphonic Etudes, op. 13. Tchaikovsky's piano sonata also shows influences of Rubinstein's Symphony no. 2, op. 42, "Ocean," Schumann's Das Paradies und die Peri, op. 50, among other compositions. The main portion of the treatise is devoted to examining a number of instances which are considered by the author to be most important and obviously in need of reconsideration. Such revisions have been undertaken with great care so that the uniqueness of the work is maintained while performing the duties Tchaikovsky would likely have done had he prepared the work for publication. The scherzo of Tchaikovsky's piano sonata served as the basis for the Scherzo of his Symphony no. 1, op. 13, and the alterations the composer made to this work guided the author in suggesting revisions and corrections to the remaining movements of the Piano Sonata. This study compares the four available editions of the work, and examines other works by the composer which date from the same period (1863-1866), in addition to the composer's Symphony no. 1, op. 13 (especially the Scherzo from that symphony). Tchaikovsky's Guide to the Practical Study of Harmony, published in 1871 is also referenced.