Proteins define the structure and function of cells. The human genome encodes tens of thousands of proteins, yet we know surprisingly little about most of their functions. The Human Protein Atlas uses labor-intensive methods to identify the tissue localization of a significant catalog of human proteins. The reasoning is that if we know where a protein is expressed, we can begin to infer roles in cellular processes. The Human Protein Atlas is an open source resource of over 15 million images that define where different proteins are located. This week's podcast discusses the Atlas with Dr. Mathias Uhlen of the University of Stockholm. We speak about the origins of the database, how the work is done, and potential applications of this incredible resource.