The article provides a comprehensive review of optical gas sensing techniques, focusing on non-dispersive infrared (NDIR), spectrophotometry, tunable diode laser spectroscopy (TDLS), and photoacoustic spectroscopy (PAS). It highlights the importance of these techniques in various applications, such as industrial processes, environmental monitoring, and atmospheric science. The review covers the fundamental principles, recent advancements, and performance limitations of each technique, emphasizing the rapid development of key components like light sources and gas cells. The authors also present a performance comparison of different techniques based on published data over the past decade, drawing conclusions from this benchmarking. The article discusses the advantages of optical gas sensing, including fast response times, minimal drift, and high gas specificity, and addresses the challenges associated with gas cell design and optical fiber coupling. Finally, it explores the use of microstructured optical fibers, hollow core waveguides, and other advanced technologies to improve gas sensing performance.The article provides a comprehensive review of optical gas sensing techniques, focusing on non-dispersive infrared (NDIR), spectrophotometry, tunable diode laser spectroscopy (TDLS), and photoacoustic spectroscopy (PAS). It highlights the importance of these techniques in various applications, such as industrial processes, environmental monitoring, and atmospheric science. The review covers the fundamental principles, recent advancements, and performance limitations of each technique, emphasizing the rapid development of key components like light sources and gas cells. The authors also present a performance comparison of different techniques based on published data over the past decade, drawing conclusions from this benchmarking. The article discusses the advantages of optical gas sensing, including fast response times, minimal drift, and high gas specificity, and addresses the challenges associated with gas cell design and optical fiber coupling. Finally, it explores the use of microstructured optical fibers, hollow core waveguides, and other advanced technologies to improve gas sensing performance.