Shyam Prabhakar, Paul Robson, Iain Beehuat Tan and colleagues characterize the cellular heterogeneity of colorectal tumors and their microenvironment on the basis of single-cell RNA–seq data analyzed with their newly developed clustering algorithm, reference component analysis (RCA). Their analyses identify two subtypes of cancer-associated fibroblasts and further divide tumors into subgroups with divergent survival probabilities.