Olof Hallonsten underestimates the status of the European Spallation Source (ESS) project and overestimates the risks to its success (Nature 518, 275; 2015).

Construction has been under way for almost six months, after Sweden and Denmark secured a combined commitment by ESS member nations to contribute more than 97% of the building costs. This commitment is underpinned by the importance of the ESS to their own national research programmes and by their prior investment in comprehensive scientific, technical and management reviews of the construction plans.

We have recruited some 300 experienced staff from around the world. More than 1,000 collaborators are bringing their collective knowledge to the project at the ESS site near Lund, Sweden, and at partner institutions in Europe.

Regarding Hallonsten's doubts about the legal and financial framework for the life cycle of the facility, a European Research Infrastructure Consortium is due to be approved this year that is set to provide such a framework.

Neither do we do deals “behind closed doors”. We have engaged more than 100 independent scientific, technical and management experts to conduct routine reviews of the project. Open meetings with the scientific community are organized twice a year. There will be risks and challenges along the way, but we are firmly committed to delivering the ESS facility on time and on budget.