vexillology

vexillology \vek-sil-AHL-uh-jee\, noun:

The study of flags.

This unknown specialist has demonstrated his great knowledge of heraldry and vexillology
-- Occasional Newsletter to Librarians, January 4, 1966

One of the most interesting phases of vexillology...is the important contribution to our heritage of flags by the Arab World.
-- Arab World, October 13, 1959

From Latin vexillum, "flag" + (Greek) -logy (from logos, " word, discourse").