Carotenoids of citrus by-products are utilized in both food and nonfood industries. Their quantification in citrus by-products depends on sample type (simple or complex), extraction process (solvent, saponification, ultrasound, microwave, etc.), and suitable quantification method (HPLC, MS, spectrophotometry, etc.). Combining the extraction and quantification methods determines the precision of carotenoid separation, identification, and quantification. This chapter focuses on different techniques and procedures for quantifying major carotenoids: β-cryptoxanthin, ζ-carotene, zeaxanthin, ζ-carotene, and violaxanthin. The primary methods for quantification include HPLC, MS, spectrophotometer, NIR, FTIR, and GC. These quantified carotenoids offer valuable antioxidants and nutritional potential for functional foods and packaging applications.