Thematic catalogs take on biblical proportions and offer exhaustive, minutely detailed entries on the primary and secondary manuscripts, first and subsequent early editions, and secondary manifestations of a composer's creative work, usually arranged chronologically or by genre, accompanied by thematic incipits for the work, its movements and other major divisions, or individual songs and pieces. The numbering system established for a composer's works often starts with a distinctive identifying initial or shortened form of the original compiler's last name or an acronym based on the catalog's title. These identifying numbers may appear alone or work in tandem with the system of opus numbers assigned by the composer.
The call no. for thematic catalogs almost always begins with ML134 followed by the initial and numeric equivalent of the composer's last name to form a browsable alphabetic sequence of volumes. Most are located in Mendel's SV (reference) collection. Thematic catalogs are generally in the language of the composer's homeland, and more recently some are bilingual publications.To date, only a small number of current thematic catalogs are available online.