The basics of McStas was written in 1997 at Risø for simulation of their neutron experiments, that were based at the DR3 reactor that was shut down in year 2000. After the fusion of Risø with the Technical University of Denmark, McStas is currently developed at the Physics department of DTU and Institut Laue-Langevin, with involvement from the Niels Bohr Institute and Paul Scherrer Institute. The Copenhagen -based Data Management and Software Centre of the European Spallation Source is also expected to become a partner since many of the future instruments are being simulated using McStas.