The senescence-associated secretory phenotype (SASP) has recently emerged as both a driver of, and promising therapeutic target for, multiple age-related conditions, ranging from neurodegeneration to cancer. The complexity of the SASP, typically monitored by a few dozen secreted proteins, has been greatly underappreciated, and a small set of factors cannot explain the diverse phenotypes it produces in vivo. Here, we present 'SASP Atlas', a comprehensive proteomic database of soluble and exosome SASP factors originating from multiple senescence inducers and cell types. Each profile consists of hundreds of largely distinct proteins, but also includes a subset of proteins elevated in all SASPs. Based on our analyses, we propose several candidate biomarkers of cellular senescence, including GDF15, STC1 and SERPINs. This resource will facilitate identification of proteins that drive specific senescence-associated phenotypes and catalog potential senescence biomarkers to assess the burden, originating stimulus and tissue of senescent cells in vivo. Figure 4. Renal epithelial cells and fibroblasts express distinct sSASPs. A) Venn diagram comparing proteins increased in the sSASP of senescent fibroblasts vs senescent epithelial cells induced by X-irradiation. B) Venn diagram comparing protein increases in the fibroblast sSASP vs decreases in the epithelial sSASP. C) Pathway and network analysis of proteins highly secreted by senescent fibroblasts and epithelial cells. C) Pathway and network analysis of proteins significantly increased in the fibroblast sSASP but significantly decreased in the epithelial cell sSASP.