Doubling rules are guidelines that dictate which notes can be doubled in a musical texture, particularly in four-part harmony, to maintain voice independence and tonal clarity. These rules help composers and arrangers avoid conflicts in harmony, which can lead to muddiness or ambiguity in the overall sound. Understanding these rules is essential for creating effective SATB (Soprano, Alto, Tenor, Bass) arrangements, as they guide the placement of notes within chords and their respective voices.