The “immunopeptidome” refers to the vast array of peptides presented at the cell surface by Major Histocompatibility Complex (MHC) molecules. These immunopeptides, derived from proteins produced or endocytosed by cells, allow immune cells such as T cells to monitor antigen presenting cells and respond when cells are diseased, such as in cancer or infection. Understanding the immunopeptidome is therefore vital for characterising immunogenic peptides, comprehending and predicting immune responses, and informing the design of effective novel immunotherapies and vaccines. Our laboratory studies the immunopeptidome by purifying MHC molecules from cells, separating out the immunopeptides and identifying them directly by mass spectrometry, and has amassed a significant body of experimental data. We have developed a knowledgebase named Haplodome for interrogating our archived data, thus extending its usefulness beyond the original experiments. The data were searched using PEAKS Studio X and the results uploaded to Haplodome’s MySQL database. To date, Haplodome contains 96 experiments with human immunopeptides purified from >40 alleles in 28 cell lines/samples, totalling 136533 unique peptide sequences at a 5% False Discovery Rate. Haplodome provides statistics and graphs to summarise the data, including breakdowns by MHC allele restriction. Users can easily search Haplodome by specific peptide sequences, modifications or experimental details, or view Haplodome immunopeptides aligned to specific protein sequences. Haplodome also facilitates deep data interrogation, including spectral viewing for peptide-spectrum matches and comparing experiments to find shared peptides. Various pages allow data export for further offline investigation. The current in-house version of Haplodome has already proven to be a useful database and toolkit for our laboratory. In the near future, we plan to release the knowledgebase, incorporate publically available datasets, and invite others to contribute. We envisage that Haplodome will be a valuable resource that contributes to a deepening knowledge and understanding of the immunopeptidome.