The article provides information on the origin of the practice of alternatim, or the alternation of two different groups of musicians in church singing. The antiphonal chanting of the psalms are the earliest instances of alternatim in the church singing. The Gregorian chant may also be sung using the alternatim alternative. The alternation of Gregorian chant and polyphony is another opportunity for alternatim. Another option in alternatim practice is between choir and organ.