Isothiocyanate is an organic compounds containing N=C=S in their chemical structure. Isothiocyanates are reactive compounds, particularly with respect to nucleophilic attack at the electron deficient central carbon atom. The chemistry of these molecules is dominated by two modes of reactions nucleophilic addition and cycloaddition. Naturally occurring isothiocyanates such as allyl isothiocyanate also known as Mustard oils are limited in number. Many of isothiocyanates, both natural and synthetic, display anticarcinogenic activity. Certain isothiocyanates have also been shown to bind to the mutated proteins found in many types of tumors. In this book several approaches for the preparation of isothiocyanates have been collected in brief.