Emblematic of the profound sense of outrage at the killing of George Floyd, Breonna Taylor, and countless other Black men and women at the hands of law enforcement, hundreds of thousands of protestors took to the streets in the USA and across the globe. They set aside the risk of contracting SARS-CoV-2, judging that what they were marching for was more immediately urgent. Marches have been held to draw attention to the continued murder by police of Black people and to the persistent, pervasive racism that exists across societies.George Floyd was killed while unarmed, handcuffed, and lying prone by a white police officer, in Minneapolis, MN, on May 25. His death once again underlines the disproportionate danger faced by Black Americans—Black men face an estimated one in 1000 chance of being killed by police over their lifetime. Solidarity and horror have been widespread.Racism is a public health emergency of global concern. It is the root cause of continued disparities in death and disease between Black and white people in the USA. Black people aged 18–34 years have higher mortality rates than white people for eight of the ten leading causes of death, including heart disease, cancer, cerebrovascular disease, diabetes, homicide, and HIV. Racism causes long-term psychological harms and illness. Repeated exposure to incidents of police killings in the media—including television and social media—can cause mental ill-health among Black American adults. The mass incarceration of Black men also leads to health inequalities.Structural racism—the structuring of a society that excludes large numbers of people from minority backgrounds from taking their full part in social institutions—operating through self-perpetuating, reinforcing systems in health care, housing, education, employment, welfare, and criminal justice, underlies the problem. These issues are rooted in centuries of discrimination and are woven into the fabric of American society. Righting them will require a whole-of-society response; the diversity of protesters who have taken part in the hundreds of informal as well as formal marches in towns and cities stretching over more than 10 days since Floyd's death on Memorial Day give cause for hope. The voices of those who have suffered racism in American society and activist movements such as Black Lives Matter must be central to bringing about change—however, all of us have a responsibility to act now.In health and medicine, associations such as the American Medical Association and the American Public Health Association have condemned racism and the killing of African Americans. These comments are welcome, but they and we must go further. We must provide details of the concrete actions we will take to correct these injustices. White Coats For Black Lives, a US medical student organisation, has recommended the promotion of recruitment and support of Black, Latino, and Native American medical students. It has also called for doctors and students to be made aware of the manifestations of racism in medicine, principles of anti-racism, and strategies for dismantling structural racism. For the individual doctor and health-care worker, it is incumbent on us all to speak out, support, and protest in any way we can. Visible non-violent protest is more likely to bring change.What can medical journals do? Our task is to educate ourselves and others about racism. We must support Black and minority ethnic health workers. And we must use evidence and our values to speak out for Black and minority ethnic communities. The Lancet is a journal with a deep colonial history: the journal has published work that supported the health of settler colonialists and that prioritised their health over those who were dominated and oppressed. We need not only to acknowledge this history, but also to find ways to use science as an instrument for social change. We pledge our solidarity with the Black Lives Matter movement. But we must now turn that pledge into concrete actions in our own work, through the research we publish, the authors we commission, and the individuals we choose to profile and recognise. We have a long way to go to fulfil these objectives. But we will.“I can't breathe”. These were the last words of George Floyd. They stand as an indictment of the pervasive oppression he and his community have faced and continue to face. These words also stand for the pervasive oppression inflicted on all marginalised people of colour. Those working in science, medicine, and public health must be representative of the societies they seek to help. But more than that, we have a duty to seek equality as a matter of justice and rights. Anti-racism is a struggle that everybody must join.For more on racism and health inequities in the USA see https://www.thelancet.com/series/america-equity-equality-in-health