The protests are a mass mobilisation against President Donald Trump's policies on immigration, education and security that organisers say are pushing the country toward autocracy.
Big and little, in cities, suburbs and small towns across the US, the protests follow mass demonstrations in June and reflect the frustration of opponents of an agenda that Trump has rolled out with unprecedented speed since taking office in January.
Saturday's rallies started outside the US, with a couple of hundred protesters gathering outside the US embassy in London, and roughly hundreds more holding demonstrations in Madrid and Barcelona.
By Saturday morning in Northern Virginia, many protesters were walking on overpasses across roads heading into Washington, DC, and several hundred people gathered in the circle near Arlington National Cemetery, near where Trump is considering building an arch across the bridge from the Lincoln Memorial.
Since Trump took office 10 months ago, his administration has ramped up immigration enforcement, moved to slash the federal workforce and cut funding to elite universities over issues including pro-Palestinian protests against Israel's war in Gaza, campus diversity and transgender policies.
Residents in some major cities have seen National Guard troops sent in by the president, who argues they are needed to protect immigration agents and to help combat crime.
"There is nothing more American than saying 'we don't have kings' and exercising our right to peacefully protest," said Leah Greenberg, co-founder of Indivisible, a progressive organisation that is the main organiser of the No Kings marches.
Trump has said very little about Saturday's protests. But in an interview with Fox Business aired on Friday he said that "they're referring to me as a king - I'm not a king."
Dana Fisher, a professor at American University in Washington, D.C., and the author of several books on American activism, forecast that Saturday could see the largest protest turnout in modern US history - she expected that over three million people would participate, based on registrations and participation in the June events.
"The main point of this day of action is to create a sense of collective identity amongst all the people who are feeling like they are being persecuted or are anxious due to the Trump administration and its policies," Fisher said.
"It's not going to change Trump's policies. But it might embolden elected officials at all levels who are in opposition to Trump."
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