On-Line Isotope Mass Separator  The ISOLDE Radioactive Ion Beam Facility, is an on-line isotope separator facility located at heart of the CERN accelerator complex on the Franco-Swiss border. The name of the facility is an acronym for Isotope Separator On Line DEvice. Created in 1964, the ISOLDE facility started delivering radioactive ion beams to users in 1967. Originally located at the SynchroCyclotron accelerator (CERN's first ever particle accelerator), the facility has been upgraded several times most notably in 1992 when the whole facility was moved to be connected to CERN's ProtonSynchroton Booster (PSB). Entering its 6th decade of existence, ISOLDE is currently the oldest facility still in operation at CERN. From the first pioneering ISOL beams to the latest technical advances allowing for the production of the most exotic species, ISOLDE benefits a wide range of physics communities with applications covering nuclear, atomic, molecular and solid-state physics, but also biophysics and astrophysics, as well as high-precision experiments looking for physics beyond the Standard Model. The facility is operated by the ISOLDE Collaboration, comprising CERN and fifteen (mostly) European countries. As of 2019, more than 800 experimentalists around the world (including all continents) are coming to ISOLDE to perform typically 45 different experiments per year. Radioactive nuclei are produced at ISOLDE by shooting a high-energy (1.4GeV) beam of protons delivered by CERN's PSBooster accelerator on a 20 cm thick target. Several target materials are used depending on the desired final isotopes that are requested by the experimentalists. The interaction of the proton beam with the target material produces radioactive species through spallation, fragmentation and fission reactions. They are subsequently extracted from the bulk of the target material through thermal diffusion processes by heating the target to about 2000 degrees. The cocktail of produced isotopes is ultimately filtered using one of ISOLDE's two magnetic dipole mass separators to yield the desired isobar of interest. The time required for the extraction process to occur is dictated by the nature of the desired isotope and/or that of the target material and places a lower limit on the half-life of isotopes which can be produced by this method, and is typically of the order of a few milliseconds. Once extracted, the isotopes are directed either to one of several low-energy nuclear physics experiments or an isotope-harvesting area.