The HTAP_v3.1 emission mosaic is developed under the umbrella of the Task Force on Hemispheric Transport of Air Pollution (TF-HTAP) and responds to the need of the global and regional atmospheric modelling community of having a mosaic emission inventory of air pollutants that conforms to specific requirements: global coverage, long time series, spatially distributed emissions with high time resolution, and a high sectoral resolution. The mosaic approach of integrating official regional emission inventories based on locally reported data, with a global inventory based on a globally consistent methodology, allows modellers to perform simulations of a high scientific quality while also ensuring that the results remain relevant to policymakers. HTAP_v3.1 is an update of the global HTAP_v3 mosaic of anthropogenic inventories, that has been developed by integrating official inventories over specific areas (North America, Europe, Asia including China, Japan and Korea) with the independent Emissions Database for Global Atmospheric Research (EDGAR) inventory for the remaining world regions. The results are spatially and temporally distributed emissions of SO2, NOx, CO, NMVOC, NH3, PM10, PM2.5, Black Carbon (BC), and Organic Carbon (OC), with a spatial resolution of 0.1 x 0.1 degree and time intervals of months and years covering the period 2000-2020. The emissions are further disaggregated to 16 anthropogenic emitting sectors. This paper describes the methodology applied to develop such an emission mosaic, reports on source allocation, differences among existing inventories, and best practices for the mosaic compilation. One of the key strengths of the HTAP_v3 emission mosaic is its temporal coverage, enabling the analysis of emission trends over the past two decades. The development of a global emission mosaic over such long time series represents a unique product for global air quality modelling and for better-informed policy making, reflecting the community effort expended by the TF-HTAP to disentangle the complexity of transboundary transport of air pollution. The emission data are available in the following formats: 1) Time series (2000-2020) of monthly and annual emissions by sector and country as .xls files. 2) Emission gridmaps: Monthly emission (in Mg/month) gridmaps at 0.1x0.1degree resolution: one .NetCDF file per year and substance is produce including for each sector the emissions for the 12 months. Monthly gridmaps of emission fluxes (in kg/m2/s) at 0.1x0.1degree resolution: one .NetCDF file per year and substance is produce including for each sector the emission fluxes for the 12 months. Annual emission (in Mg/year) gridmaps at 0.1x0.1degree resolution: one .NetCDF file per year and substance is produce including the emissions for each sector. Annual emission (in kg/m2/s) gridmaps at 0.1x0.1degree resolution: one .NetCDF file per year and substance is produce including the emission fluxes for each sector. To facilitate data access and use, gridmaps at 0.5x0.5 degree resolution are also made available following the abovementioned specifications of the higher spatial resolution data (0.1x0.1 degree).