One expert in social movements told the BBC there is a momentum gathering among different social movements "fuelled by a level of anger I have never seen in my lifetime".
He did, however, condemn gun violence - in France. Mr Trump sent his condolences a day after a deadly supermarket attack that the French leader described as an act of Islamist terrorism.
Some of today's demonstrators waved placards insulting the US president
as they filed past his hotels in Washington DC and New York.
People walk by the Trump Hotel in New YorkImage caption: People walk by the Trump Hotel in New York
ReutersCopyright: Reuters
Protesters outside the Trump International Hotel in Washington DCImage caption: Protesters outside the Trump International Hotel in Washington DC
Recap on the day's events
In the biggest gun control protest in a generation, hundreds
of rallies were staged today in the US and overseas, with events as far afield
as London, Paris, Mauritius, Tokyo, Stockholm, Geneva and Berlin.
Marchers filled streets in American cities
including Atlanta, Baltimore, Boston, Chicago, Los Angeles, Houston, Miami, Phoenix, Minneapolis, New York, San
Diego, St Louis, Atlanta, Detroit and Parkland. A pro-gun march was also held in Helena, Montana.
This map shows the 800-plus locations where rallies were co-ordinated globally.
The focal point was Washington DC, where tens of thousands of demonstrators took to the streets in one of the biggest rallies since the Vietnam era.
One of the most emotionally charged moments came when Marjory Stoneman Douglas High School survivor Emma Gonzalez stood silent at the podium for several minutes to mark the duration of the mass shooting at her school in Parkland, Florida, the incident that ignited the #NeverAgain movement.
ReutersCopyright: Reuters
A March for Our Lives in Los Angeles, CaliforniaImage caption: A March for Our Lives in Los Angeles, California
Watch some of the global rallies
Video content
Video caption: Hear from protesters in London, Paris, Edinburgh and SydneyHear from protesters in London, Paris, Edinburgh and Sydney
Should the US arm teachers?
Hannah Snelling, 19, was a survivor of a school shooting two years ago and is now at university studying to become a teacher.
Hannah, who favours stricter gun laws and traveled from rural Ohio to Washington for the march, tells the BBC many of her class discussions are about how to protect students - not teach them.
"You can't stop violence with more violence," she said.
"My students don't need to feel like they're in a prison, but I do want metal detectors,
"When the kid shot up our school he waited for the armed officer to leave the room before he started shooting."
Conservatives
routinely pillory Hollywood stars for espousing liberal causes such as firearms
control.
They note that these same actors’ movies typically glorify gun
violence, or that they benefit from the security provided by armed guards at red carpet jamborees.
Amy Schumer
launched an impassioned rebuttal against those critics today at the Los Angeles March
for Our Lives.
She told the
crowd: "We know it’s hard and we know they will twist our words and laugh at
us, and lie and lie and lie and lie and lie. How do they sleep at night?
"You are
killing children. And they call people like me 'Hollywood liberals'. Like there’s
something in it for us.
"No, what's in
it for us is knowing we're doing our part to keep our children alive.
"Speaking up
about this puts literal targets on our backs. And for sick bullying and lies
about us, and it narrows the people who will support our work.
"We sell
half as many tickets because we’re standing up for what’s right."
Schumer spoke out about firearms violence after a gunman opened fire, killing two people, at a screening
of her movie Trainwreck in Louisiana three years ago.
She also happens to be related
to Senate Democratic leader Chuck Schumer, a vocal proponent of gun control.
Earlier, Mya Middleton spoke movingly about her experience of gun violence in Chicago.
Video content
Video caption: March For Our Lives: 'He points a pistol in my face'March For Our Lives: 'He points a pistol in my face'
Why is NRA so powerful?
NRA stands for National Rifle Association. The group was founded in 1871 as a recreational group designed to "promote and encourage rifle shooting on a scientific basis".
The NRA is now among the most powerful lobby groups in the US, with a substantial budget to influence members of Congress on gun policy. It is run by executive vice-president Wayne LaPierre.
Video content
Video caption: Why the NRA wields so much powerWhy the NRA wields so much power
Video content
Video caption: NRA and Florida: Seven things Wayne LaPierre blames after shootingNRA and Florida: Seven things Wayne LaPierre blames after shooting
A tale of two senators
The two US senators from Florida, a Republican and a Democrat, have expressed very different sentiments about today's march.
But both praised the students for standing up for what they believe in. Senator Bill Nelson, a Democrat, attended the rally in Washington.
Marco Rubio, a Republican, has faced severe public criticism over his opposition to gun control, following the massacre in his home state.
Emma Gonzalez, who brought a prolonged hush to the Washington crowd with a six-minute silence, was among the Marjory Stoneman Douglas activists featured on the cover of Time magazine this week ahead of today's march.
One of the more well-known Parkland school students, Emma Gonzalez, delivered a powerful speech in which she listed the 17 people killed before she fell silent for a few minutes.
When an alarm beeped, she turned it off and noted that six minutes and 20 seconds had passed since she first took the stage, saying they represented the exact time it took the shooter to gun down her classmates.
"The shooter has ceased shooting and will soon abandon his rifle, blend in with the students as they escape and walk free for an hour before arrest. Fight for your lives before it is someone else's job."
The crowd erupted into chants of "Emma, Emma" as she left the stage.
Kyle Kashuv challenged a classmate to a debate on the issueImage caption: Kyle Kashuv challenged a classmate to a debate on the issue
Not all the students at Marjory Stoneman Douglas High School are in favour of stricter gun laws.
Kyle Kashuv is vehemently opposed.
He says the emphasis should be on the failure of authorities to stop the Parkland shooting suspect.
The 16-year-old told Fox News today: "I talked to so many marchers and they don't have a clear-cut solution. It pains me not to see the government being held accountable for their failures.
"I don't see anyone blaming Sheriff Scott Israel for failing to do what he was supposed to do.
"I don’t see anyone looking at the FBI and saying that how come two reports weren’t followed through?
"I don’t see anyone going, ‘78 reports to the Broward sheriff’s office and nothing is done.'"
Kyle also just challenged his classmate David Hogg to a debate on the gun control issue.
Earlier this week, we spoke to a shooting coach in North Carolina who teaches young people how to safely use firearms.
Jeff Price, 50, said: "What the march really represents to me, is a moment of mourning for those who are lost in some of the most heinous things I've seen in my adult life.
"This march is a lot more of a representation of mourning for the lost. I do believe it should create an open dialogue for creating or facilitating a way to prevent things like this from happening.
"We need an open dialogue and it's not just about banning guns."
Watch the video below to hear more from Jeff and the young people he teaches.
Video content
Video caption: The American children who love shooting gunsThe American children who love shooting guns
Live Reporting
Tom Geoghegan, Jude Sheerin and Courtney Subramanian
All times stated are UK
Video caption: Gun marchers: 'Our message to the world is...'Gun marchers: 'Our message to the world is...' View more on twitterView more on twitter 
AFPCopyright: AFP People walk by the Trump Hotel in New YorkImage caption: People walk by the Trump Hotel in New York 
ReutersCopyright: Reuters Protesters outside the Trump International Hotel in Washington DCImage caption: Protesters outside the Trump International Hotel in Washington DC 
ReutersCopyright: Reuters A March for Our Lives in Los Angeles, CaliforniaImage caption: A March for Our Lives in Los Angeles, California Video caption: Hear from protesters in London, Paris, Edinburgh and SydneyHear from protesters in London, Paris, Edinburgh and Sydney Video caption: Armed teacher from Colorado: 'My biggest fear is missing'Armed teacher from Colorado: 'My biggest fear is missing' View more on twitterView more on twitter View more on twitterView more on twitter 
ReutersCopyright: Reuters View more on twitterView more on twitter Video caption: March For Our Lives: 'He points a pistol in my face'March For Our Lives: 'He points a pistol in my face' Video caption: Why the NRA wields so much powerWhy the NRA wields so much power Video caption: NRA and Florida: Seven things Wayne LaPierre blames after shootingNRA and Florida: Seven things Wayne LaPierre blames after shooting View more on twitterView more on twitter View more on twitterView more on twitter View more on twitterView more on twitter View more on twitterView more on twitter 
Getty ImagesCopyright: Getty Images View more on twitterView more on twitter View more on twitterView more on twitter 
Fox NewsCopyright: Fox News Kyle Kashuv challenged a classmate to a debate on the issueImage caption: Kyle Kashuv challenged a classmate to a debate on the issue View more on twitterView more on twitter View more on twitterView more on twitter View more on twitterView more on twitter View more on twitterView more on twitter Video caption: The American children who love shooting gunsThe American children who love shooting guns
Latest PostWhere do US protests go from here?
The #NeverAgain campaign is not a movement that exists in isolation.
By one count, there have been 15 major protests on progressive issues in the year since President Trump took office, including two Women's Marches and one against a far-right rally in Charlottesville, Virginia.
March For Our Lives brings the tally to 16.
One expert in social movements told the BBC there is a momentum gathering among different social movements "fuelled by a level of anger I have never seen in my lifetime".
Read more about where American protests go from here.
'Our message to the world is...'
BBC reporter Hannah Long-Higgins was speaking to marchers in Washington today.
Video content
What did Trump say?
Though the White House put out a statement earlier about today's protests, President Donald Trump himself has stayed largely mum.
He did, however, condemn gun violence - in France. Mr Trump sent his condolences a day after a deadly supermarket attack that the French leader described as an act of Islamist terrorism.
Some of today's demonstrators waved placards insulting the US president as they filed past his hotels in Washington DC and New York.
Recap on the day's events
In the biggest gun control protest in a generation, hundreds of rallies were staged today in the US and overseas, with events as far afield as London, Paris, Mauritius, Tokyo, Stockholm, Geneva and Berlin.
Marchers filled streets in American cities including Atlanta, Baltimore, Boston, Chicago, Los Angeles, Houston, Miami, Phoenix, Minneapolis, New York, San Diego, St Louis, Atlanta, Detroit and Parkland. A pro-gun march was also held in Helena, Montana.
This map shows the 800-plus locations where rallies were co-ordinated globally.
The focal point was Washington DC, where tens of thousands of demonstrators took to the streets in one of the biggest rallies since the Vietnam era.
One of the most emotionally charged moments came when Marjory Stoneman Douglas High School survivor Emma Gonzalez stood silent at the podium for several minutes to mark the duration of the mass shooting at her school in Parkland, Florida, the incident that ignited the #NeverAgain movement.
Watch some of the global rallies
Video content
Should the US arm teachers?
Hannah Snelling, 19, was a survivor of a school shooting two years ago and is now at university studying to become a teacher.
Hannah, who favours stricter gun laws and traveled from rural Ohio to Washington for the march, tells the BBC many of her class discussions are about how to protect students - not teach them.
"You can't stop violence with more violence," she said.
"My students don't need to feel like they're in a prison, but I do want metal detectors,
"When the kid shot up our school he waited for the armed officer to leave the room before he started shooting."
Read more about whether arming teachers could help prevent future bloodshed.
Video content
Every child killed remembered
'Speaking up puts literal targets on our backs'
Conservatives routinely pillory Hollywood stars for espousing liberal causes such as firearms control.
They note that these same actors’ movies typically glorify gun violence, or that they benefit from the security provided by armed guards at red carpet jamborees.
Amy Schumer launched an impassioned rebuttal against those critics today at the Los Angeles March for Our Lives.
She told the crowd: "We know it’s hard and we know they will twist our words and laugh at us, and lie and lie and lie and lie and lie. How do they sleep at night?
"You are killing children. And they call people like me 'Hollywood liberals'. Like there’s something in it for us.
"No, what's in it for us is knowing we're doing our part to keep our children alive.
"Speaking up about this puts literal targets on our backs. And for sick bullying and lies about us, and it narrows the people who will support our work.
"We sell half as many tickets because we’re standing up for what’s right."
Schumer spoke out about firearms violence after a gunman opened fire, killing two people, at a screening of her movie Trainwreck in Louisiana three years ago.
She also happens to be related to Senate Democratic leader Chuck Schumer, a vocal proponent of gun control.
The 11-year-old girl with a rallying cry
Naomi Wadler is only 11 - but her strong voice at the March for Our Lives rally in Washington, DC, is still reverberating across the US.
The fifth grader from Alexandria, Virginia, said she represented African-American girls ignored by the media and suffering from gun violence.
Read more about the girl who inspired Americans with her speech at the March for Our Lives.
'Why I'm not marching'
'Chicago goes through this every day'
Earlier, Mya Middleton spoke movingly about her experience of gun violence in Chicago.
Video content
Why is NRA so powerful?
NRA stands for National Rifle Association. The group was founded in 1871 as a recreational group designed to "promote and encourage rifle shooting on a scientific basis".
The NRA is now among the most powerful lobby groups in the US, with a substantial budget to influence members of Congress on gun policy. It is run by executive vice-president Wayne LaPierre.
Video content
Video content
A tale of two senators
The two US senators from Florida, a Republican and a Democrat, have expressed very different sentiments about today's march.
But both praised the students for standing up for what they believe in. Senator Bill Nelson, a Democrat, attended the rally in Washington.
Marco Rubio, a Republican, has faced severe public criticism over his opposition to gun control, following the massacre in his home state.
Republican Senator Marco Rubio pointed out that not all Americans support gun restriction.
Bird's-eye view of DC crowds
Cover boys and girls
Emma Gonzalez, who brought a prolonged hush to the Washington crowd with a six-minute silence, was among the Marjory Stoneman Douglas activists featured on the cover of Time magazine this week ahead of today's march.
Six minutes and 20 seconds
One of the more well-known Parkland school students, Emma Gonzalez, delivered a powerful speech in which she listed the 17 people killed before she fell silent for a few minutes.
When an alarm beeped, she turned it off and noted that six minutes and 20 seconds had passed since she first took the stage, saying they represented the exact time it took the shooter to gun down her classmates.
"The shooter has ceased shooting and will soon abandon his rifle, blend in with the students as they escape and walk free for an hour before arrest. Fight for your lives before it is someone else's job."
The crowd erupted into chants of "Emma, Emma" as she left the stage.
Aerial footage from US rallies - CNN
Parkland voice against gun control
Not all the students at Marjory Stoneman Douglas High School are in favour of stricter gun laws.
Kyle Kashuv is vehemently opposed.
He says the emphasis should be on the failure of authorities to stop the Parkland shooting suspect.
The 16-year-old told Fox News today: "I talked to so many marchers and they don't have a clear-cut solution. It pains me not to see the government being held accountable for their failures.
"I don't see anyone blaming Sheriff Scott Israel for failing to do what he was supposed to do.
"I don’t see anyone looking at the FBI and saying that how come two reports weren’t followed through?
"I don’t see anyone going, ‘78 reports to the Broward sheriff’s office and nothing is done.'"
Kyle also just challenged his classmate David Hogg to a debate on the gun control issue.
Kyle recently met the president and first lady in the Oval Office.
Here's Kyle's interview with Fox News earlier:
Martin Luther King Jr's granddaughter speaks
The civil rights icon's granddaughter led the crowd in Washington with an inspiring chant.
“I have a dream that enough is enough,” she said. “And that this should be a gun free world, period.”
She asked the crowd to repeat her words:
“Spread the word”
“Have you heard?”
“All across the nation”
“We are going to be a great generation.”
Banning guns 'not the answer'
Earlier this week, we spoke to a shooting coach in North Carolina who teaches young people how to safely use firearms.
Jeff Price, 50, said: "What the march really represents to me, is a moment of mourning for those who are lost in some of the most heinous things I've seen in my adult life.
"This march is a lot more of a representation of mourning for the lost. I do believe it should create an open dialogue for creating or facilitating a way to prevent things like this from happening.
"We need an open dialogue and it's not just about banning guns."
Watch the video below to hear more from Jeff and the young people he teaches.
Video content