The first and foremost duty of an Oral Pathologist or any general dentist is to detect a premalignant lesion sufficiently early to prevent their progress to invasive carcinoma. Though final diagnosis always should be given on the basis of laboratory-based investigations which sometimes are associated with variable false-negative rates, but Toluidine blue vital staining can serve as an important chair side investigation in detecting prompt premalignant lesion. Its feasibility rate is high since it is simple, inexpensive and sensitive in nature. Chemically Toluidine blue is a basic thiazine metachromatic dye having high affinity for acidic tissue components like DNA and RNA thus serves in detecting tissues rich in former mentioned proteins. It's metachromatic property leads its wide applications both as vital staining in living tissues and as a special stain. So it is being used often in vivo to identify dysplasia and carcinoma of the oral cavity. Its aim is to highlight components, such as mast cells granules, mucins, and cartilage. Thus this article will shed some light on principle, basic technique, its necessity and the various applications of toluidine blue.