The SysteMHC Atlas project aims at collecting, organizing and sharing major histocompatibility complex (MHC) immunopeptidomic data generated by mass spectrometry. The Atlas includes raw mass spectrometer output files, context-specific datasets of MHC class I and class II peptides and standardized MHC allele-specific peptide spectral libraries. The Atlas is linked to the PRIDE proteomics identification database, the Immune Epitope Database (IEDB), and the SWATHAtlas database. The SysteMHC computational infrastructure and website will be continuously developed toward a high quality community-driven global mapping of the mouse and human immunopeptidome. Achieving the vision of a baseline immunopeptidome will facilitate navigation of robust quantitative digital maps of immunopeptidomes in the future to support the consistent measurement of immunopeptidomic sample cohorts.