The Human Protein Atlas (HPA) is a Swedish-based program started in 2003 with the aim to map all the human proteins in cells, tissues and organs using integration of various omics technologies, including antibody-based imaging, mass spectrometry-based proteomics, transcriptomics and systems biology. All the data in the knowledge resource is open access to allow scientists both in academia and industry to freely access the data for exploration of the human proteome. In November 2020, version 20 was launched along with a celebratory publication of the 20 year history of HPA. Version 20 introduces an additional sub-atlas, the Single Cell Type Atlas, showing expression of protein-coding genes in single human cell types, in addition to the existing sub-atlases; the Tissue Atlas showing the dist