The Boy Scouts say they will now admit girls. Here’s what that means.

The Boy Scouts board of directors said Wednesday it would open some of its programs to girls, including the path to the prestigious title of Eagle Scout, the organization’s highest rank.

The change marks a major shift for the century-old establishment. The Boy Scouts of America said its decision is an important evolution in how it meet the needs of families and their children, but the move has previously sparked criticism from the female-focused Girl Scouts of the USA.

Here’s what we know about the decision — and what it means for scouting.

The new plan: Starting next year, the Boy Scouts will create separate boys and girls Cub Scout dens, its smallest unit. Those dens can be combined to create Cub Scout packs. Older girls may enter a new program as early as 2019 which will qualify them for the Eagle Scout rank.

Girls were previously able to participate in certain existing programs, including the Venturing and Sea Scouts, but could not pursue the Eagle Scout ranking. Many girls have tried to join Boy Scouts over the years, all unsuccessfully, The New York Times noted as it chronicled a group of five California girls trying to join the organization in 2015.

Another girl, Sydney Ireland, attracted media attention earlier this year for being an unofficial boy scout in Manhattan’s Troop 414, something she’s done since she was four years old. Ireland told WNYC that she regularly went with her brother to Cub Scout meetings. Today, Ireland, 16, has petitioned the Boy Scouts to allow her and other girls to become official members.

In a Change.org petition, Ireland explained why she thought girls ought to be allowed into Boy Scouts:

“I cannot change my gender to fit the Boy Scouts’ standards, but the Boy Scouts can change their standards to include me. I am determined to be an Eagle Scout. It isn’t just a hobby, it’s access to some of the best leadership training there is,” she wrote. “Unfortunately for me and half the country’s population, we are excluded from most of these amazing opportunities for no reason other than that we are female. That’s why I’m calling on the BSA to end the discriminatory ban against young women and girls, and allow all children to participate in the Boy Scouts and earn the Eagle Rank.”

Why the policy changed: The Boy Scouts of America said it made the decision based on months of research and information from girls, parents and members of the institution.

“The values of Scouting – trustworthy, loyal, helpful, kind, brave and reverent, for example – are important for both young men and women,” said Boy Scouts chief scout executive Michael Surbaugh said in a statement. “We strive to bring what our organization does best – developing character and leadership for young people – to as many families and youth as possible as we help shape the next generation of leaders.”

The organization has faced criticism for years on its positions on sexual orientation and gender (as chronicled here by the Los Angeles Times). Today’s announcement comes on the heels of the Boy Scouts’ decision in January to allow transgender participants. The group ended its controversial ban on openly gay scouts in 2013 and on gay Boy Scout leaders in 2015.

“The Boy Scouts say their decision is informed by research from over the summer and the months proceeding,” said New York Times reporter Niraj Chokshi, who spoke with Girl Scout leadership following Wednesday’s announcement. But the Girl Scouts were “blindsided by the decision,” Chokshi said.

What about the Girl Scouts? Both the Boy and Girl Scouts emerged out of World War I and have historically maintained a close relationship. But, in August, a letter was made public in which the president of the Girls Scouts accused the Boy Scouts of a “covert campaign to recruit girls” and undercut Girl Scout participants.

“I formally request that your organization stay focused on serving the 90 percent of American boys not currently participating in Boy Scouts,” Kathy Hopinkah Hannan, the president of the Girl Scouts, wrote to Boy Scouts president Randall Stephenson.

The letter calls the Boy Scouts of America “reckless” in “thinking that running a program specifically tailored to boys can simply be translated to girls.”

In a statement released Wednesday night, the Girl Scouts said “At Girl Scouts, we are the girl experts, and for more than a century we have provided millions of girls opportunities for adventure, inspiration, and valuable mentoring.”

It continues:

The benefit of the single-gender environment has been well-documented by educators, scholars, other girl- and youth-serving organizations, and Girl Scouts and their families. Girl Scouts offers a one-of-a-kind experience for girls with a program tailored specifically to their unique developmental needs.

How many Boy and Girl Scouts are there? There were 1.8 million Girl Scouts in 2015, and 2.3 million Boy Scouts in 2016.

Boy Scout participation is down from 2.6 million in 2013, with about 4 million in the early 2000s. Girl Scout total membership — including youth members and adult volunteers — dropped 11.6 percent from 2012 to 2014. It has dropped 3.8 million members, or 27 percent, since 2003.

“More than 100,000 Scouting units are owned and operated by chartered organizations,” according to the Boy Scouts website — 70 percent of them by faith-based organizations, which have at times been criticized for placing too much emphasis on religious beliefs.

How are the programs different? Aside from the groups’ gender divide, a 2011 Sage Journal Gender and Society study found that Boy Scouts are led away from artistic interests, while Girl Scouts are discouraged from scientific studies, though the Girl Scouts have been increasing focus on science and math in recent years. This year, it added 23 new STEM and outdoor badges. Additionally, Girl Scout activities are more group-oriented, while Boy Scouts are more often individual.

The highest award for Girl Scouts is a Gold Award, which fewer than 6 percent of Girl Scouts achieve. Boy Scout’s highest rank is that of Eagle Scout. About 5 percent of Boy Scouts, more than 2 million, have earned the Eagle Scout rank since 1912.

“The Boy Scouts would argue that the skills they teach boys will apply to both girls and boys,” Chokshi said. However, Chokshi said the dens are still single gender and the lack of description for the older girls’ program leaves questions unanswered. Also, older groups could decide to be single gender, as could the dens.

What’s next? Supporters of the decision applauded the Boy Scouts of America on its inclusiveness and holding to its main values to support youth needs.

The Church of Jesus Christ of Latter-Day Saints, whose congregations are major sponsors of Boy Scout troops, said in a statement that they “recognize that the desire of the BSA is to expand their programs to serve more young people in the United States.”

“The Church, too, continues to look at ways to serve the needs of our youth worldwide,” Mormon Church spokesman Eric Hawkins told the PBS NewsHour.

“Kiwanis International and Boy Scouts of America have a strong partnership that goes back to the 1950s. We share a priority in our work to shape the next generation of leaders,” Stan Soderstrom, executive director of Kiwanis International, said in an email to the NewsHour. Kiwanis partners with the Boy Scouts, with clubs sponsoring 710 units of scouts and more than 18,000 youths. Soderstrom told the NewsHour that the organization “values inclusiveness and looks forward to continuing our partnership with Boy Scouts of America.”

Meanwhile, the Girl Scouts say “the need for female leadership has never been clearer or more urgent than it is today—and only Girl Scouts has the expertise to give girls and young women the tools they need for success.”

“We’re committed to preparing the next generation of women leaders, and we’re here to stay,” the group’s statement says.

“The Girl Scouts see it as a threat to their territory and the Boy Scouts are saying ‘we are offering another option,’” Chokshi said. “Depending on how it plays out, we will see how targeted it was at the Girl Scouts.”