Melanoma is a lethal type of skin tumor that has been linked with sunlight exposure. Wavelengths from the sun that can reach the earth's surface include UVA radiation (320-400 nm) and UVB radiation (280-320 nm). UVB effectively induces the formation of dimeric DNA photoproducts, preferentially the cyclobutane pyrimidine dimers (CPDs). The characteristic UVB signature mutations in the form of C to T mutations at dipyrimidine sequences are prevalent in melanoma tumor genomes and can be ascribed to deamination of cytosines within CPDs before DNA polymerase bypass. However, evidence from epidemiological, animal, and other experimental studies, although somewhat controversial, also suggest that UVA radiation may participate in melanoma formation. The DNA damage relevant for UVA includes specific types of CPDs at TT sequences and perhaps oxidative DNA damage to guanine. We have been applying sensitive methodologies for genome-wide mapping of different types of DNA damage in human skin cells and have been using these approaches for linking UV-induced DNA damage and mutations to melanoma-specific mutational signatures.