Though it’s been nearly 20 years since the Human Genome Project provided a blueprint for human biology, it still left much work to be done to understand health and disease at a molecular level. The Sweden-based Human Protein Atlas, which is seeking to map human proteins in cells, tissues, and organs, recently published significant updates to the open-access resource. We spoke to Mathias Uhlén, director of the Human Protein Atlas, about how the atlas is changing the diagnosis and treatment of disease, what’s known about the human proteome to date, and how this understanding will be essential to brining about an era of precision medicine.