A general analytical approach for scaling NOx, emissions from burners and furnaces is presented, together with the scaling model for NOx emissions performance that results when this approach is applied to a broad class of swirl-stabilized industrial gas burners. The model is based on results from a sea of collaborative burner scaling experiments on a generic gas burner and furnace design at five different scales having near-uniform geometric, aerodynamic. and thermal similarity and uniform measurement protocols. This collaborative effort provides the first NOx scaling data over the range of thermal scales from 30 kW to 12 MW, including input-output measurements as well as detailed in-flame measurements of NO, NO2, CO, O-2, unburned hydrocarbons, temperature, and velocities at each scale. The in-flame measurements allow identification of keg; sources of NOx production. The underlying physics of these NOx sources lead to scaling laws for their respective contributions to the overall NOx emissions performance. It is found that the relative importance of each source depends on the burner scale and operating conditions. The scalings fur these NOx sources are combined in a comprehensive scaling model for NOx emission performance. Results from the scaling model show good agreement with experimental data at all burner scales and over the entire range of turndown, staging, preheat, and excess air dilution, with correlations generally exceeding 90%. The scaling model permits design trade-off assessments for a broad class of burners and furnaces, and allows performance of full industrial-scale burners and furnaces of this type to be inferred from results of small-scale tests.