ABSTRACT Helicases are being ubiquitous in nature, has the property to break the hydrogen bonds between annealed nucleotide bases and used to separate strands of a DNA, RNA molecule. They are also being used in separation of the double-stranded RNA and RNA–DNA hybrids. In bacteria, helicases regulates different functions like DNA replication, repair, recombination, and transcription. The DnaB, primary replicative helicase involved in bacterial DNA replication. It helps to unwind the DNA duplex as well as attracting the DnaG primase towards the replication fork so that replication can start. It is known that DEAD-box and DEAH-box RNA helicases are involved in many processes including the modification of RNA secondary structures. They help in intermolecular RNA and RNA/protein interactions. Bacterial DEAD-box proteins regulate the ribosome biogenesis, RNA decay and translation initiation. Based on sequence information and protein structures RNA and DNA helicases are divided into six superfamilies All RNA helicases and some DNA helicases are present in SF1 and SF2 groups. SF3-6 group contains other DNA helicases, translocases, and AAA + proteins. RNA unwinding, removing of protein from RNA, RNA annealing, RNA-dependent ATPase, metabolite sensing, and RNA clamping are some major biochemical characteristics of DEAD-box helicases. In bacteria, DEAD-box are the key molecules that are required in many adverse conditions like for growth at low temperature, in low biofilm condition, providing resistance in oxidative stress, reduced catalase activity, upregulation of some genes, prey-independent growth condition, and reduced growth in iron deficient conditions. Now days, helicases are emerging as important targets for the generation of novel antiviral, antibiotic, and anticancer drugs. In this chapter, we will review about DNA and RNA helicases and their role in different developmental processes and stress responses.