This book covers the various approaches of Vilsmeier–Haack reaction and their synthetic applications. The work of the book is devoted to a study of a series of organic reactions which employs Vilsmeier–Haack reaction to synthesize various heterocyclic derivatives. Vilsmeier–Haack reaction is a key step for the conversion of various functional groups to desire group/moiety. Recent advances in the Vilsmeier–Haack reaction is elaborated with their wide range of synthetic applications that may help the researchers for future endeavor in organic synthesis. Improved and modified conditions applied during the path of DMF (Dimethylformamide) and POCl3 (Phosphoryl chloride) reagents herein demonstrates with the application of conversion of particular functional groups in presence of other. The book summarizes important reactions and recent involvement of Vilsmeier–Haack reagent along with its possible outcome in organic chemistry.