Activator protein-1 (AP1) is a dimeric protein, consisting either of homodimers between c-Jun, JunB, and JunD of by heterodimers with members of the Fos-family by physically interacting via a "leucine zipper" region. AP1 is an important transcription factor initially identified as a DNA binding protein that bound to enhancer sequences of the human metallothionein IIA gene. The protein components of AP1 are encoded by a set of genes known as "immediate-early" genes that can be activated by a variety of growth factors and mitogens through several different signaling pathways. Until recently, AP1 was considered a transcription factor expressed in most tissues to regulate cellular and viral genes now, it is becoming evident that AP1 can be involved in tissue-specific regulation of target genes due to the differential combination of the components of this important transcription factor. AP1 plays a crucial role during human papillomavirus (HPV) early gene expression, in particular of the expression of E6 and E7 oncoproteins. The HPV are a group of DNA viruses consisting of more than 80 different genotypes. Some of these HPV, know as high risk HPV, are important etiologic agents of uterine-cervical cancer (CaCu). Of the different types of cancer, CaCu is one of the most frequent among women worldwide, constituting the second death cause due to neoplasia. During cellular transformation, HPV infect basal cells in stratified epithelium; their DNA integrate into the host genome usually through the E2 gene; as these cells differentiate and migrate into the upper layer of the epithelium, viral oncogene are expressed blocking their differentiation. Mutagenesis in AP1 sites belonging to the HPV promoter region (LCR) completely abolished the HPV promoter activity in different cell lines; these results and biochemistry assays on this AP1 transcription factor, that includes protein-protein interactions between AP1 and another factors as E7 from HPV, and YY-1; the post-translattional modification and, the retinoic acid interaction; suggest a role for this AP1 factor in tissue-specific transcription of the human papillomavirus.