Thousands of scientists have taken part in demonstrations around the world in protest against what they see as a global political assault on facts.
The first-ever March for Science, which was timed to coincide with Earth Day, was aimed at promoting action to protect the environment.
Organisers said it was a celebration of science and a call to support and safeguard the scientific community.
The main event was held in Washington DC.
The event's promoters said the march in the US capital was not aimed against President Donald Trump, while adding that his administration had "catalysed" the movement.
At the demonstration in Washington DC, Dr Jonathan Foley, the executive director of the California Academy of Sciences, said that research was being irrationally questioned, adding that attacks from politicians "amounted to oppression".
"They're specifically targeting science that protects our health, our safety and the environment. Science that protects the most vulnerable among us," he said.
"Some people will suffer, some could even die," Dr Foley added.
From climate change and pollution to medicine, men and women who support science were motivated on Saturday by the coverage of the recent Women's March and are mobilising to make their concerns heard.
Organisers of the March for Science Vienna, in Austria, earlier said on the group's Facebook page that it was encouraging people to turn out to join a movement that began shortly after Mr Trump entered the White House.
Mr Trump has previously called climate change a hoax and his views have raised concerns among the scientific community that the public are beginning to doubt the facts provided as scientific evidence.
In London, scientists and science enthusiasts marched from the Science Museum to Parliament Square.
Many were protesting against what they consider to be an "alarming trend" among politicians for discrediting their research.
The aim of the March for Science was to bring scientists and their research closer to the general public.
Organisers are of the view that it can be challenging for scientists to communicate with the public and are even actively encouraging scientists to become politicians so that their voices can be effectively heard.