This overview document presents incidents where aid workers were reportedly arrested or detained by state or non-state actors (‘authority action’). The report is based on incidents identified by Insecurity Insight's monitoring of open sources and reported by Aid in Danger partner agencies using the Security in Numbers Database (SiND). In 2017, 136 aid workers were arrested or detained in 76 incidents in 27 countries. For full figures by month and country see HDX Insecurity Insight. Data collection is ongoing and data may change as more information is made available.