Infrared gas sensing， based on the characteristic infrared absorption of gas molecules， provides an optical approach for gas identification and concentration quantification. It has found broad applications in environmental monitoring， industrial safety， breath analysis， remote sensing， and other fields. Driven by the growing demand for miniaturized， integrated， and multi-component detection systems， the performance of infrared gas sensors is no longer determined by individual device optimization alone， but increasingly depends on the coordinated design of light sources， gas-light interaction structures， detectors， and spectral models. This review summarizes recent advances in infrared gas sensing from the perspective of system-level design and key enabling technologies. The evolution of light sources from broadband incoherent emitters to lasers and frequency combs is first discussed. Gas-light interaction structures， including free-space gas cells， hollow-core fibers， and on-chip waveguides， are then reviewed. Detector technologies are summarized in terms of photon， thermal， and photoacoustic detection mechanisms. In addition， spectral modeling methods for information extraction， including sampling optimization， multivariate regression， and machine learning， are discussed. Finally， future directions toward high sensitivity， multi-component analysis， miniaturization， intelligent sensing， and on-chip integration are outlined.