Newsweek:

Though the public is not permitted to check books out of the Library of Congress, legislators may remove the library's books for as long as they want. As a result, many volumes have been missing for decades; an estimated 30,000 of the library's 16.4 million books are gone and considered stolen. Among the missing: two $7,500 collections of nineteenth-century Italian architectural drawings, a $6,000 nineteenth-century treatise on cactuses, two $1,500 volumes on Navajo rituals, and Abbie Hoffman's Steal This Book.

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