Irmologion (Greek: εἱρμολόγιον (heirmologion)) is a liturgical book of the Eastern Orthodox Church and those Eastern Catholic Churches which follow the Byzantine Rite, and it contains texts for liturgical singing in Church. Specifically, it contains irmoi (introductory hymns) for the various canons which are chanted at Matins and other services. The word derives from the words εἱρμός (heirmos) meaning "link" i.e. an introductory stanza and λογεύω (logeuō) meaning "to collect". Within the Irmologion, the irmoi are arranged according to the eight tones of Byzantine chant.