Organism experiences different types of environmental conditions like nutrient starvation, biotic and abiotic stress condition. So for their survivility they need to adjust themselves for outside conditions. Hence, for their existence they make use of variety of biopolymers like nucleic acid as a cell instructor, protein as a catalyst and carbohydrates as energy pockets. Beside the role of mRNA as template for translation, it is also recognized that RNA play regulatory role in gene expression. Beginning of this decade had identified 5‟ UTR of mRNA molecule that sense metabolite and regulate the gene expression. Such RNA molecules are referred as metabolite sensing non coding RNA molecule or riboswitch. This book give valuable information on Riboswitches and How it regulates gene expression.