Optical gas sensing is a critical technology for detecting and measuring gas concentrations, with applications ranging from industrial processes to environmental monitoring. This review discusses various gas detection techniques, including non-dispersive infrared (NDIR), spectrophotometry, tunable diode laser spectroscopy (TDLS), and photoacoustic spectroscopy (PAS). These methods rely on the optical absorption properties of gases, offering fast response times, minimal drift, and high specificity. The review highlights recent advancements in light sources, gas cells, and detection systems, and compares the performance of different techniques based on data from the past decade. Gas detection technologies include traditional methods like gas chromatography and semiconductor sensors, which are less sensitive and have limitations in cross-response and drift. In contrast, optical gas sensors provide high accuracy and reliability, with the ability to measure in real-time without disturbing the sample. The Beer-Lambert Law is fundamental to optical gas sensing, relating light absorption to gas concentration. The review also discusses the challenges of measuring low concentrations and the importance of calibration and environmental factors. Optical gas cells are designed to optimize signal detection, with configurations such as long path cells, hollow core fibers, and integrating spheres. These cells are crucial for achieving high sensitivity and accuracy. The review also addresses the use of optical fibers for remote sensing, enabling the deployment of sensors in hazardous environments. Microstructured optical fibers, such as photonic crystal fibers, offer advantages in gas sensing due to their ability to confine light and interact with gas molecules. Non-dispersive infrared (NDIR) sensors are widely used for detecting gases like carbon dioxide, with their simplicity and cost-effectiveness. These sensors use broadband sources and reference channels to minimize background interference. The review discusses the performance of NDIR sensors, including their detection limits and response times, and highlights the importance of source and detector optimization for improved performance. The review concludes that optical gas sensing offers a reliable and efficient solution for gas detection, with ongoing advancements in technology improving sensitivity, accuracy, and practicality. The integration of optical fibers and microstructured fibers is expected to further enhance the capabilities of gas sensing systems, enabling more widespread and effective monitoring of gas concentrations in various applications.Optical gas sensing is a critical technology for detecting and measuring gas concentrations, with applications ranging from industrial processes to environmental monitoring. This review discusses various gas detection techniques, including non-dispersive infrared (NDIR), spectrophotometry, tunable diode laser spectroscopy (TDLS), and photoacoustic spectroscopy (PAS). These methods rely on the optical absorption properties of gases, offering fast response times, minimal drift, and high specificity. The review highlights recent advancements in light sources, gas cells, and detection systems, and compares the performance of different techniques based on data from the past decade. Gas detection technologies include traditional methods like gas chromatography and semiconductor sensors, which are less sensitive and have limitations in cross-response and drift. In contrast, optical gas sensors provide high accuracy and reliability, with the ability to measure in real-time without disturbing the sample. The Beer-Lambert Law is fundamental to optical gas sensing, relating light absorption to gas concentration. The review also discusses the challenges of measuring low concentrations and the importance of calibration and environmental factors. Optical gas cells are designed to optimize signal detection, with configurations such as long path cells, hollow core fibers, and integrating spheres. These cells are crucial for achieving high sensitivity and accuracy. The review also addresses the use of optical fibers for remote sensing, enabling the deployment of sensors in hazardous environments. Microstructured optical fibers, such as photonic crystal fibers, offer advantages in gas sensing due to their ability to confine light and interact with gas molecules. Non-dispersive infrared (NDIR) sensors are widely used for detecting gases like carbon dioxide, with their simplicity and cost-effectiveness. These sensors use broadband sources and reference channels to minimize background interference. The review discusses the performance of NDIR sensors, including their detection limits and response times, and highlights the importance of source and detector optimization for improved performance. The review concludes that optical gas sensing offers a reliable and efficient solution for gas detection, with ongoing advancements in technology improving sensitivity, accuracy, and practicality. The integration of optical fibers and microstructured fibers is expected to further enhance the capabilities of gas sensing systems, enabling more widespread and effective monitoring of gas concentrations in various applications.