Lineage tracing is the identification of all progeny of a single cell. Although its origins date back to developmental biology of invertebrates in the 19(th) century, lineage tracing is now an essential tool for studying stem cell properties in adult mammalian tissues. Lineage tracing provides a powerful means of understanding tissue development, homeostasis, and disease, especially when it is combined with experimental manipulation of signals regulating cell-fate decisions. Recently, the combination of inducible recombinases, multicolor reporter constructs, and live-cell imaging has provided unprecedented insights into stem cell biology. Here we discuss the different experimental strategies currently available for lineage tracing, their associated caveats, and new opportunities to integrate lineage tracing with the monitoring of intracellular signaling pathways.