The Tabula Muris Senis is a comprehensive resource for the cell biology community which offers a detailed molecular and cell-type specific portrait of aging. We view such cell atlas as an essential companion to the genome: the genome provides a blueprint for the organism but does not explain how genes are used in a cell type specific manner or how the usage of genes changes over the lifetime of the organism. The cell atlas provides a deep characterization of phenotype and physiology and serves as a reference for understanding many aspects of the cell biological changes that mammals undergo during their lifespan. The project includes single-cell and bulk RNA-sequencing of different organs across the mouse lifespan.