Ruth F. Boorstin, the stalwart collaborator with and editor of her late husband, former librarian of Congress and prize-winning historian Daniel J. Boorstin, died Dec. 1 at an assisted-living center in Encino, Calif. She was 95.

The cause was sudden cardiopulmonary arrest, said a granddaughter, Julia Boorstin Samuelson.

Mrs. Boorstin was a published poet and for decades a prominent member of Washington society. She came to the District when her husband was named director of the Smithsonian Institution’s National Museum of History and Technology, now the National Museum of American History, in 1969.

He became librarian of Congress in 1975 and held the post until 1987.

People who knew the Boorstins, Washington Post staff writer Sarah Booth Conroy once observed, came to regard the bookish couple as “being forever joined by an invisible ampersand.”

Ruth F. Boorstin, shown here with husband Daniel J. Boorstin, was a stalwart collaborator and editor of her late spouse, a prize-winning historian. (Family Photo)

Daniel Boorstin, who died in 2004, described his wife as his “principal and most penetrating editor.” She sharpened and refined his vast output of historical volumes, which included “The Americans: The Democratic Experience,” the winner of the 1974 Pulitzer Prize for history.

“Without her,” he observed, “I think my works would have been twice as long and half as readable.”

Ruth Boorstin, for her part, told The Post: “I clean his pipes and shape his books.” She said she considered herself and her husband fortunate because many other couples did not enjoy the commonality of interests that they had.

Her name appeared with his on the cover of “The Landmark History of the American People” (1987). In addition to her editorial work, Mrs. Boorstin was credited with helping her husband create the Center for the Book, an initiative established by the Library of Congress to promote books and literacy around the country.

Ruth Carolyn Frankel was born Dec. 16, 1917, in Morenci, Ariz. Her father was a copper-mining engineer and her mother was a teacher. She grew up in New York and in 1938 received a bachelor’s degree in economics from Wellesley College in Massachusetts. Three years later, she met and married her husband.

Mrs. Boorstin reviewed books for the New York Times and other newspapers in the 1940s. In the 1950s and ’60s, during her husband’s teaching career at the University of Chicago, she created and edited a syndicated newspaper column featuring children’s creative writing. In 1964, she received a master’s degree in the social sciences from the University of Chicago.

Before settling in Washington, she accompanied her husband on academic posts in Italy, France, Puerto Rico and Japan. They lived for several decades in Cleveland Park and had a second home, called Mount Vernon View, in Accokeek, Md.

Among other civic engagements, Mrs. Boorstin served on the Corcoran Gallery of Art’s board of trustees, the Smithsonian Institution’s women’s board and the advisory board of the Reading Is Fundamental literacy organization, said her granddaughter.

Survivors include three sons, Paul Boorstin of Beverly Hills, Calif., Jonathan Boorstin of Studio City, Calif., and David Boorstin of New York City; six grandchildren; and a great-grandson.

Mrs. Boorstin regularly published poetry in the Wall Street Journal and collected her works in the volume “Love Is Not Because” (1998). One of her verses went:

How nice it is to have a mate

And intimately collaborate

With an editorial we

To make an us of him and me.