San Francisco ? Browsing through sections marked “muckraking,” “anarchism” and “stolen continents” may be unnerving to an unsuspecting book buyer, but it’s exactly what draws patrons to City Lights Books.

The North Beach institution, made famous in the 1950s as a center for the Beat movement, celebrates a half-century in business this month. And staff and outside experts agree the store, which began in a hallway and the basement and now consumes the entire building, is stronger than ever.

“We’ve become an international cultural center,” says Nancy Peters, who co-owns City Lights with poet Lawrence Ferlinghetti. “People come here because they know we have great books, but we also have political discussions and readings.”

About 50,000 books are crammed into 2,200-square-feet of retail space. The books are packed tightly onto tall, wooden shelves on wheels. With stacks placed at unusual angles, it’s not a store for “roaming the aisles.” But there are reading nooks and other spots to sit and relax.

Political posters dominate the walls. A “Viva Zapata” poster hangs on one wall; a poster commemorating author Eduardo Galeano hangs on another. Hand-lettered signs are everywhere: “No Shirt. No Shoes. Full Service”; “Stash Your Cell Phone and Be Here Now”; “Have a Seat and Read a Book.”

Fiction dominates the main floor. Some best sellers are stocked — “The Hours,” “Atonement” and “Life of Pi” — but they’re not prominently displayed. One huge shelf contains staff-recommended reading. “The Corrections,” by Jonathan Franzen, is there, but so is “Mabinogion Tetralogy,” by Evangeline Walton, and “The Few Things I Know About Glafkos Thrassakis,” by Vassilis Vassilikos — not exactly hot sellers.

A scary, rickety stairway leads to the lower level, swollen with books about history, science, politics and travel. That’s where you’d find “stolen continents” books — works about American imperialism.

The third floor is dedicated to the Beat writers and poetry.

“We’re not that influenced by market forces,” said buyer Paul Yamazaki, who started working at City Lights in 1970, packing and shipping books. “Books aren’t product to us. We have a real knowledge and passion for what’s on our shelves. That’s the key.”

Ferlinghetti and sociology teacher Peter D. Martin pitched in $500 each and opened City Lights in 1953 in a former flower shop. It helped launch the Beat movement in 1956 by publishing Allen Ginsburg’s “Howl,” which led to Ferlinghetti’s arrest on obscenity charges. He was later acquitted.

The store remained controversial. In 1961, City Lights Publishers released the Journal for the Protection of all Beings, an early ecology magazine. In 1966, the store again was raided, this time for selling Lenore Kandel’s purportedly obscene “The Love Book.”