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[Display omitted] • Comprehensive review of 2D transition metal dichalcogenides (TMDs) based gas sensors. • Approaches to develop room temperature gas sensors. • Strategies to fabricate low power and highly selective 2D materials-based gas sensor. • Discussion of different strategies such as doped, decorated and composite 2D MoS2 and MoSe2-based gas sensors. • Detailed explanation of gas sensing mechanisms of gas sensors. The goal of current research in gas sensor technology is the development of a highly effective, small gas sensor that is able to operate at room temperature. There has been a surge in interest in 2D nanomaterials for the fabrication of high-performance gas sensor devices after graphene because of the exceptional physical, chemical, optical, and electrical properties of two-dimensional semiconductor nanomaterials. Among various 2D nanomaterials, we are focusing on transition metal dichalcogenides (TMDs) used for the fabrication of room temperature (RT) gas sensors because of their high surface area, large surface activity, extremely high carrier mobility, narrow bandgap, and high conductivity. Molybdenum disulfide (MoS 2) and molybdenum diselenide (MoSe 2), a well-researched TMDs, have drawn considerable attention across diverse domains for gas sensing materials at RT due to their intriguing two-dimensional layered structures and electrochemical features. The fabrication of chemiresistor sensors using MoS 2 and MoSe 2 has shown immense promise in meeting present-day demands, highlighting the remarkable technological advancements over the last several decades. It is anticipated that the strategic modification of the surface of MoS 2 and MoSe 2 nanomaterials using the decoration of nanoparticles will play a key role in the development of nanomaterials with unique chemical and physical properties as well as catalytic power, allowing them to boost the overall performance of gas sensors at RT. Herein, this review article provides an in-depth overview of the latest advancements made in MoS 2 and MoSe 2 nanomaterial-based chemiresistive gas sensors for the sensing of toxic gases at RT. Initially, we outline the method for synthesis and growth of MoS 2 and MoSe 2 nanomaterials, and the basic principles of sensing mechanisms are elucidated, relying on the charge transfer dynamics between gas species and MoS 2 and MoSe 2 nanomaterials. Furthermore, this article examines the current developments in the performance of gas sensors based on MoS 2 and MoSe 2 nanomaterials through the combination of nanocomposites, van der Waals heterostructures, doping, and decoration of nanoparticles, as well as their capabilities in sensing gases. Finally, this review offers insights into numerous emerging challenges and potential avenues for future research on gas sensor technologies utilising diverse 2D MoS 2 and MoSe 2 nanomaterials. [ABSTRACT FROM AUTHOR]