The Watermelon library is a high complexity lentiviral barcode library for simultaneous tracing of clonal lineages as well as the transcriptional and proliferative state of each cell in the population. Lineage tracing is achieved by mapping a clone-specific expressed DNA barcode in the 3′ untranslated region of an mNeonGreen protein, and proliferation history is monitored by the dilution of a doxycycline (dox)-inducible H2B-mCherry transgene.