Hayden is credited with modernizing the Enoch Pratt Free Library, Baltimore’s 22-branch city library system. (She also successfully kept the library open throughout the Freddie Gray protests last year.) As president of the American Library Association in 2003 and 2004, she frequently and publicly criticized Section 215 of the USA Patriot Act, which allowed federal law enforcement to access public-library borrowing records.

Hayden has sat on the National Museum and Library Services Board since 2010. She holds a doctorate degree in library sciences from the University of Chicago. Though these may sound like job requirements, Hayden is the first professional librarian to run the Library in more than 60 years.

(After Billington’s retirement, many professional librarians called for a librarian to take over the institution, instead of a historian or public intellectual.)

She inherits a library that desperately requires an update. A report from the Government Accountability Office last year found that the Library, once a leader in adapting to the internet, had fallen behind the times and needed to update its aging computer systems.

Hayden was confirmed 74-18 by the Senate. All of the dissenting senators were Republicans, including Senators Mark Kirk, Ted Cruz, Marco Rubio, and Tom Cotton. And though she was unanimously endorsed by the G.O.P-controlled Senate Rules Committee, an anonymous Republican senator blocked the vote to confirm Hayden’s appointment for more than five weeks.

By contrast, James Billington was unanimously confirmed by a Democratic-majority Senate in 1987. The Washington Post reported the block on Tuesday.

Hayden’s time as Librarian will be limited to 10 years, as mandated by a law passed by Congress last autumn.

When measured by number of books and other collected materials, the Library of Congress is the second-largest library in the world. Containing more than 160 million items, it is more than double the size of the third-largest institution, the Library and Archives of Canada. The British Library is the world’s largest.

By law, the Library of Congress receives two copies of every copyright-protected work published in the United States. These items form the basis of its collection, but its core offerings can be traced back more than two centuries, to the country’s founding fathers. After invading British troops burned the first Library during the War of 1812, the federal government purchased former president Thomas Jefferson’s personal collection—more than 6,000 books—to form the basis of its new one. Some of those tomes are still catalogued in Washington, D.C., today.

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