The Fagradalsfjall volcanic system is one of six volcanic systems on the Reykjanes Volcanic Zone. In the literature Fagradalsfjall volcanic system has either been classified as an individual system or a secondary volcanic swarm on the neighbouring Krýsuvík volcanic system. An eruption started on the system on March 19th in 2021, following more than a year of earthquake activity and inflation/deflation periods. This eruption put an end to ca. 800 years of volcanic quiescence on the Reykjanes peninsula and defines the beginning of a new eruptive period on the Reykjanes Volcanic Zone. It was also the first eruption on the Fagradalsfjall system in about 6000 years. About 10 postglacial eruptions are known from the system, all older than 6000 years. The volcanic system is located between the Svartsengi and Krýsuvík volcanic systems and differs from the other systems in the Reykjanes Volcanic Zone as it includes neither a subaerial geothermal field nor a NE-SW trending fissure swarm. However, there are N-S trending tectonic faults. The characteristic volcanism formations are lava shields, of which one of the largest ones is Þráinsskjöldur. The highest point of the volcanic system is within the Fagradalsfjall tuya (ca. 390 m a.s.l.), after which the system is named. The characteristic activity is effusive basaltic but size estimation of individual lava flows is hard as they are partly covered by younger formations. The system has erupted twice after volcanic activity resumed (in 2021 CE and 2022 CE). The first eruption lasted for six months and filled in a pre-existing valley landscape, covering 4,85 km2 with 0,15 km3 of lava. The second one lasted for about three weeks and added 0,01 km3 on top of the older lava covering an area of 1,3 km2. The largest known eruption in Fagradalsfjall volcanic system is the formation of a shield volcano of a few km3 in volume. One such eruption has occurred in the last 14,000 years. Such an eruption is considered unlikely at present time.