Historical Aspects of Xeroderma Pigmentosum and Nucleotide Excision Repair -- Clinical Features of Xeroderma Pigmentosum -- Xeroderma Pigmentosum and Skin Cancer -- XPA Gene, Its Product and Biological Roles -- XPB and XPD between Transcription and DNA Repair -- XPC: Its Product and Biological Roles -- The XPE Gene of Xeroderma Pigmentosum, Its Product and Biological Roles -- XPF/ERCC4 and ERCC1: Their Products and Biological Roles -- XPG: Its Products and Biological Roles -- Xeroderma Pigmentosum Variant, XP-V: Its Product and Biological Roles -- Other Proteins Interacting with XP Proteins -- The Nucleotide Excision Repair of DNA in Human Cells and Its Association with Xeroderma Pigmentosum -- Roles of Oxidative Stress in Xeroderma Pigmentosum -- Xeroderma Pigmentosum: Its Overlap with Trichothiodystrophy, Cockayne Syndrome and Other Progeroid Syndromes -- Population Distribution of Xeroderma Pigmentosum -- Progress and Prospects of Xeroderma Pigmentosum Therapy -- Animal Models of Xeroderma Pigmentosum. Xeroderma pigmentosum (XP), meaning parchment skin and pigmentary dist- bance, is a rare and mostly autosomal recessive genetic disorder that was originally named by two dermatologists, the Austrian Ferdinand Ritter von Hebra and his H- garian son in law Moritz Kaposi in 1874i and 1883. 2 The earliest published record (PubMed) available on the internet is a publication in 1949 by Ulicna Zapletalova under the title, "Contribution to the pathogenesis of xeroderma pigmentosum". ^ It was in the late 1960s when James Cleaver (contributor of Chapter 1 of this book), at the University of California, San Francisco, while working on nucleotide excision repair (NER), read an article in a local newspaper about XP and soon after obtained a skin biopsy from a patient suffering from XP that showed that cells from it were deficient in NER. Thus, his studies led to the discovery that indeed this genetic defect was due to mutations in DNA repair genes that imbalance the NER pathway. ^. s The discovery paved the way for further exploration of the link between DNA damage, mutagenesis, neoplastic transformation and DNA repair diseases. Since then, 4,088 papers, incl- ing excellent reviews, on XP are listed on the internet (PubMed data, February 2008), and an XP Society has been established in the USA (http://www. xps. org) and an XP Support Group in the United Kingdom (www. xpsupportgroup. org. uk).