The reliable, selective, and fast detection of the inorganic and organic gases in indoor and outdoor air and industrial processes is a huge challenge for environmental sustainability, healthier life, and disease control and diagnosis. Metal oxides have been frequently explored as highly sensitive receptor elements in the electronic gas sensors since the 1960s. Gallium oxide (Ga₂O₃), often recognized as one of the widest-bandgap semiconductors, has shown tremendous potential as the inorganic gas receptor because of its extraordinary chemical and thermal stability, and excellent electronic properties. This article presents a comprehensive reference on the electrical properties, historical developments, detection mechanisms, and gas sensing performance of Ga₂O₃ nanowires and composite nanostructures. In particular, the relationships between composition, nanostructure, and gas sensing properties of gallium-containing oxidic nanomaterials such as β-Ga₂O₃ nanowires, surface-modified Ga₂O₃, metal-doped Ga₂O₃ or Ga-doped metal oxides, and Ga₂O₃/metal oxide composite heterostructures are studied. The applications of Ga₂O₃ gas sensors are discussed with an emphasis on their practical limitations such as high-temperature operation, power consumption, and miniaturization issues. Finally, future research directions and potential developments are suggested.