Georgius Prenner, born around 1530 in Ljubljana, is a less known but important sixteenth century composer. The Supplementa 3 is an addition to the volume XXIV of the series Monumenta artis musicæ Sloveniæ containing Prenner's motets. It brings three yet unknown and historically interesting adaptations of original vocal pieces for keyboard instruments (in the so called organ tablature) that survived in two Bavarian manuscript anthologies. The introductory text contains some yet unknown details on the composer's life and work. The author of the edition, Dr Marko Motnik, contributed his realization of pieces in modern notation in two systems, an exhaustive introduction and editorial explanations and comments.