O_ASSEN - Eurasian oystercatchers (Haematopus ostralegus, Haematopodidae) breeding in Assen (the Netherlands) is a bird tracking dataset published by the Vogelwerkgroep Assen, Netherlands Institute of Ecology (NIOO-KNAW), Sovon, Radboud University, the University of Amsterdam and the Research Institute for Nature and Forest (INBO). It contains animal tracking data collected for the study O_ASSEN using trackers developed by the University of Amsterdam Bird Tracking System (UvA-BiTS, http://www.uva-bits.nl). The study has been operational in 2018 and 2019. In total 6 individuals of Eurasian oystercatchers (Haematopus ostralegus) have been tagged as a breeding bird in the city of Assen (the Netherlands), mainly to study space use of oystercatchers breeding in urban areas.