The biologist toolbox has expanded over the last century. It is now common to describe a phenotype using an arsenal of single-cell sequencing and mass spectrometry-based technologies as well as advanced imaging methods. More recently, the merging of single-cell genomics and lineage-tracing innovations has allowed researchers to access cellular ancestry information at unprecedented scale. Applied across systems and scales, cellular phylogenetics is revealing novel insights on developmental dynamics, disease origins and therapeutic responses. This is likely just the tip of the iceberg. As with previous methodological breakthroughs, cellular phylogenetics may hold the potential to revolutionize entire fields and help us engineer enhanced cell therapies. Throughout this talk we will discuss the breadth of findings so far and, through examples of our own, we will cover what we have learned about the biology of blood development, regeneration, aging and cancer.