Since April 2022, cases of simian orthopoxvirosis (commonly known as monkeypox) have been reported in more than hundred non-endemic countries. The causative agent, the Monkeypox virus (MPXV), is a virus of the family Poxviridae belonging to the genus Orthopoxvirus (OPXV). The sudden and unusual emergence of this virus mainly in Europe and in the United States has highlighted a previously neglected infectious disease. This virus has been endemic in Africa for at least several decades, since its discovery in 1958 in captive monkeys. MPXV, because of its proximity to the smallpox virus, is part of the list of Microorganisms and Toxins (MOT), which includes all human pathogens considered to be potentially misused for malicious purposes (biological weapons proliferation, bioterrorism) or susceptible to provoke laboratory accidents. As such, its use is subjected to strict regulations in level-3 biosafety laboratories, which de facto limits the possibilities of its study in France. The objective of this article is to review the current knowledge about OPXV in general, and then to focus on the virus responsible for the 2022 MPXV outbreak.