In this chapter, the principles and techniques of different optical probes used in the detection and quantification of food adulterants have been described with emphasis on infrared (IR) spectroscopy. The IR spectroscopy provides rapid detection and quantification of a variety of adulterants in common food items such as milk, honey, cooking oil, spices, flour, etc. For example, the distinctive 1140 cm−1 peak in FTIR spectrum of turmeric powder indicates the presence of metanil, a common adulterant.