Open societies have benefited immeasurably from an influx of international scientists. The rapid exchange of ideas and expertise depends upon such movement, as do innovation and economic growth. It is therefore extremely worrying to read reports of Chinese scientists in the United States being treated unfairly (see Nature 571, 157; 2019).

About one-quarter of US National Academy of Sciences members and one-quarter of US Nobel prizewinners were born abroad — and many more are children of immigrants. Three of the past five presidents of the Royal Society in London came from overseas, myself included: I’m an Indian-born US and British national.

Appropriate immigration controls, national security, local laws and ethical norms must all be taken seriously. But ‘innocent until proven guilty’ is an axiom of law throughout the civilized world. Guilt should never be assumed on the basis of national origin or religious belief, or on a perceived association. Actions such as the internment of US citizens of Japanese descent during the Second World War or the blacklisting of actual or alleged communists during the McCarthy era are now considered shameful episodes in US history.

We scientists must stand up for openness and fairness. Discriminating against someone because of their ethnicity, turning down a collaboration or refusing a visa for a conference on the grounds of nationality, or simply making someone feel unwelcome because they are an immigrant — these are all morally objectionable and practically counterproductive. Such behaviour must cease.