Dyes are synthetic organic chemicals that are either water or oil soluble; however, pigments are insoluble and exist in particulate form. Organic dyes are utilized in several industrial applications, including textile (the most prominent), food items, cosmetics, and paper printing, resulting in their common presence in industrial effluent. This chapter provides the detailed discussion about cationic (Rhodamine B, Methylene blue, Methyl violet, Malachite green, Crystal violet, and Brilliant green) and anionic dyes (Methyl orange, Congo red, Eriochrome black T, Rose Bengal, Eosin Y, and Indigo Carmine) with their structures and properties.