On Saturday, activists in Washington, D.C. and across the country will hold “March for Our Lives” rallies to protest gun violence. The rallies were planned in response to the mass shooting last month at Marjory Stoneman Douglas High School in Parkland, Florida,but they’ve quickly grown into a global initiative. Now, there are 838 marches planned worldwide. Here’s a guide to the main U.S. march in the nation’s capital.

Who are the organizers? Student activists from Marjory Stoneman Douglas High School are helping lead the march in Washington, D.C., and students at other schools around the country holding similar rallies Saturday. The events were planned in collaboration with larger gun reform organizations like Everytown for Gun Safety.

Who is marching? Student activists from Washington to Indianapolis — where high school students are protesting a rise in local homicides — to Los Angeles, where a number of celebrities are expected to attend a rally. According to the March for Our Lives website, there will also be official marches in a number of countries, from Italy to India and Ghana. American students have also organized marches in Austria and Spain.

Who is funding the rallies? Celebrities like Oprah Winfrey, Justin Bieber, Steven Spielberg and George and Amal Clooney, who donated $500,000, provided a significant portion of the funding. The overall cost for the rally in Washington is unclear, but by comparison, the Women’s March on Washington last year raised more than $2 million through direct donations. Organizers have said that all of the donations would go towards covering the expenses for the Washington march, including the permits to hold the event as well as lobbying efforts, voter registration and ballot initiatives.

What are they trying to achieve? While gun control advocates have a broad-ranging agenda, most have focused on pushing for comprehensive gun reform legislation that they say would prevent mass shootings. Organizers have also zeroed in on school safety, and are calling for lawmakers to ensure there are no mass shootings inside schools in the future.

“The march on Saturday means that we are on our way to getting real common sense gun safety done,” Fred Guttenberg, whose 14-year-old daughter Jaime was killed in the Parkland shooting, told the PBS NewsHour’s Judy Woodruff on Thursday night. “It means that, in a very short period of time, these kids and the people of this country have stepped up and spoken up and said, enough. And I think what you’re going to see is, not just in Washington, but around the country, possibly the largest number of people ever marching.”