The CIA announced Wednesday that it is ending the publication of its long-running World Factbook, a widely used reference guide detailing countries’ economies, militaries, resources, and societies.

First launched in 1962 as a classified manual for intelligence officers, the Factbook was made unclassified within a decade and became an essential resource for other federal agencies. In 1997, it went online, quickly gaining popularity among journalists, trivia enthusiasts, and students writing research papers.

The CIA’s website offered no explanation for the decision, though it comes amid Director John Ratcliffe’s stated goal of ending programs that do not directly advance the agency’s core missions. The move also follows White House efforts to reduce staffing at the CIA and National Security Agency early in President Trump’s second term, forcing intelligence agencies to operate with leaner teams.

Despite its popularity, the CIA did not respond to requests for comment regarding the cessation of the World Factbook.