An Irmologion is a liturgical book of the Eastern Orthodox Church and of some Eastern Rite Catholic Churches. It contains texts for singing in church called irmoi (introductory hymns, and sometimes concluding ones) for canons chanted at Matins and other services throughout the liturgical year. The term Irmologion comes from the Greek words for “link” and “to collect.” Rozniki (chants used for some specific occasions, such as Christmas and Easter) were mostly sung in Old Believer communities, who rejected 17th century reforms in the official Russian Orthodox Church. This work was compiled between the mid-16th century and the 1720s and is in Church Slavonic, then the most widely used church ceremonial language in Eastern Orthodoxy. Its hook and znamenny (a word derived from the Russian for “marks” or “banners”) musical notation was a Russian development from Byzantine notation. The main characteristic of this system is that it records melodic transitions and encodes the musical mood (tenderness, strength, tempo, and so forth), rather than specific notes. The script is in semi-uncial, small letters. Three types of handwriting from three different time period are discernible, with differing watermarks of variable degrees of visibility. Folios 9−141, dating from about the 1550s to about 1625, show the first type of handwriting and a watermark of a small pitcher with one handle, with a crown on the lid, topped by a four-lobed rosette. The second kind of writing appears in folios 143−66 verso, dating from circa 1625 to the mid-17th century, with watermarks barely discernible. The third type of writing, on folios 168−288 verso, dates from the mid-17th century. These folios have two watermarks: a small two-handled pitcher and a bouquet of leaves, with a small three-lobed lily on the top and letters on the side; and the same small two-handled pitcher, with a crown on the lid topped by a crescent moon, without letters and with thicker handles. Most of the leaves written later than the main manuscript (folios 1−8, 142, 167, 271, and 289−91, approximately 1675−1725) are bound in at the beginning and the end of the book and have as a watermark one of two different pictures of the coat of arms of Amsterdam. This work is preserved at the National Library of Karelia, Russia.