Janice Killian, Michael O’Hern and Linda Rann. The sister series, designed to be used alongside the Essential Musicianship tutor books for choirs, these volumes contain a wide variety of songs from different historical periods, other countries and cultures, English and foreign-language texts, levels and styles, from masterworks, folksongs and spirituals, a cappella and accompanied pieces, sacred and secular works and some pop-style selections.