Gas sensors are widely utilized in industrial environments for safety purposes, but their applications also include ventilators, residential and automotive security systems, and surveillance technologies. They show potential for clinical applications and are crucial to the growing Internet of Things (IoT). To address the demands of various industrial settings, it is crucial to develop sensors that are quick, sensitive, selective, reliable, and cost-effective. This chapter explores different gas sensor technologies, such as electrochemical, optical, catalytic, thermal conductivity, and acoustic sensors, and describes their fundamental principles of operation. Enhancements in gas sensor performance can be achieved through methods such as doping sensing materials, reducing particle size to the nanoscale and advancing sensor design. Important factors like morphology, nano-structuring, and the introduction of dopants that modify the crystallographic structure of the sensing material are vital for improving gas sensing capabilities and are influenced by synthesis techniques. The chapter also discusses how various physical and chemical attributes—such as crystallography, geometry, size, surface functionalization, and bulk doping—impact gas sensing performance, drawing from existing research.