The article describes the characteristics of sources of polyphonic music up to circa 1500 preserved in Poland. Their number is at present estimated to be 72 manuscripts (some 47 of which may be regarded as closely related to the Polish culture). Predominant among them are entries of polyphonic compositions in liturgical or non-musical codices (60%), and fragments (26%). Research into them thus faces a variety of methodological problems. The author demonstrates their nature using two previously unknown minor sources of polyphonic music as examples. He also discusses selected paradigms of interpreting Polish musical culture of the fifteenth century.