This unit describes the theory and detailed protocols for performing in vivo lineage tracing from Lgr5(+ve) intestinal stem cells using an Lgr5-EGFP-ires-CreERT2/Rosa26lacZ mouse model. Lineage tracing can be initiated in mice at any age by administering limiting doses of the hormone tamoxifen. This activates the lacZ reporter gene in the Lgr5(+ve) stem cells, which subsequently transmit this permanent genetic mark to their progeny as they repopulate the epithelium during normal homeostasis. Because the Lgr5(+ve) cells are long-lived, self-renewing stem cells, they continuously generate lacZ progeny, which contribute to tissue renewal over the entire lifetime of the mouse. The same protocols can be applied to performing in vivo lineage tracing from other Lgr5(+ve) stem cell populations, including those in the hair-follicle and stomach.