Gas-involving　cancer　theranostics　have　attracted　considerable　attention　in　recent　years　due　to　their　high　therapeutic　efficacy　and　biosafety.　We　have　reviewed　the　recent　significant　advances　in　the　development　of　stimuli-responsive　gas　releasing　molecules　(GRMs)　and　gas　nanogenerators　for　cancer　bioimaging,　targeted　and　controlled　gas　therapy,　and　gas-sensitized　synergistic　therapy.　We　have　focused　on　gases　with　known　anticancer　effects,　such　as　oxygen　(O2),　carbon　monoxide　(CO),　nitric　oxide　(NO),　hydrogen　sulfide　(H2S),　hydrogen　(H2),　sulfur　dioxide　(SO2),　carbon　dioxide　(CO2),　and　heavy　gases　that　act　via　the　gas-generating　process.　The　GRMs　and　gas　nanogenerators　for　each　gas　have　been　described　in　terms　of　the　stimulation　method,　followed　by　their　applications　in　ultrasound　and　multimodal　imaging,　and　finally　their　primary　and　synergistic　actions　with　other　cancer　therapeutic　modalities.　The　current　challenges　and　future　possibilities　of　gas　therapy　and　imaging　vis-à-vis　clinical　translation　have　also　been　discussed.　Copyright　©　2019　American　Chemical　Society.