This contribution tries to explain the exceptional decision by the Swiss Federal Council to reject the Institutional Agreement (InstA).

The first part reviews the motivations of the seven Federal Councillors and the pressures to which they were subjected, even from political forces that are not far-right nationalists or traditional Eurosceptics.

The second part highlights the radical nature of the decision to reject the InstA, given that:

- the agreement had been relatively well negotiated by Switzerland,

- the EU had made substantial concessions and had not been particularly intransigent,

- the last remaining obstacles seemed to have been exaggerated and could have been overcome by domestic measures in Switzerland

- and, finally, the harmful consequences of a rejection of the InstA were well known.