Although yellow, flavonol-based dyes were widely used in pre-modern times, this class of natural dyes presents special problems because flavonols (3-hydroxyflavones) readily undergo photo-oxidation, resulting in fading or discoloration. However, if the 3-hydroxy group is substituted, e.g. with a glycosyl group, the flavonol derivative is relatively stable. We analyzed representatives of eight plant genera, Delphinium, Flaveria, Pistachia, Prangos, Rhamnus, Sophora, Tamarix and Vitis, with the aim of identifying the flavonol components present. In all cases, the principal colorants were flavonol 3-O-glucosides (or, in one case, 3-O-sulfates), although some plants also contained the light-labile flavonol aglycones. We discuss some strategies that can be and may have been used to reduce the concentration of flavonol aglycones. In addition the identification of specific flavonol glycosidesm, or their high performance liquid chronmatography elution patternsm, is usedcul in identifying the plants used to dye ancient textiles, for shich historical records are absent.