Thousands of people are expected to attend March for Science events around the world to promote the understanding of science and defend it from various attacks, including U.S. government budget cuts.
The March for Science was dreamed up at the Women's March on Washington, a day after U.S. President Donald Trump's inauguration in January. Saturday is also Earth Day.
The march puts scientists, who generally shy away from advocacy and whose work depends on objective experimentation, into a more public position.
Scientists involved in the march said they are anxious about political and public rejection of established science such as climate change and the safety of vaccines.
In Germany, scientists were expected to rally in more than a dozen cities including Berlin, Bonn, Dresden and Hamburg.
The group Evidence for Democracy lists more than dozen planned rallies across Canada on its website, including events in Toronto and Vancouver.
With files from The Canadian Press