(CNN) -

Harper Lee's "To Kill a Mockingbird" celebrates its 54th birthday Friday, and for the first time, it's available as an e-book.

Since it was published July 11, 1960, the Pulitzer Prize-winning novel has sold more than 30 million copies worldwide and been translated into 50 languages. In 1999, it was voted best novel of the 20th century by Library Journal. Until this week, though, it had never been available as an e-book.

The story

"To Kill a Mockingbird" is a coming-of-age story about two children in the South, Scout and Jem Finch. While their lawyer father, Atticus, defends Tom Robinson, a black man wrongly accused of rape, the children are fascinated by a mysterious neighbor, Boo Radley. Through the trial and their experiences in their hometown of Maycomb, Alabama, Scout and Jem learn about racism and acceptance in the 1930s Deep South.

The author

Born in 1926, Lee spent her childhood in Alabama before moving to New York when she was 23. She struggled with odd jobs over the years and, in 1956, decided to write full time. She found a publisher interested in her novel and completed it three years later.

In "Mockingbird," a 2006 biography about Lee, author Charles J. Shields, wrote that the novel is partially autobiographical, based on Lee's childhood in Monroeville, Alabama. Similar to the young protagonist in "To Kill A Mockingbird," Lee was a tomboy whose father was a lawyer.

The town where the novel takes place is based on her hometown, and the fictional trial in "Mockingbird" closely parallels the 1931 Alabama "Scottsboro Boys" trial.

Lee has said that although she didn't want the trial in her book to be as sensational, her intent was to expose the longstanding racial disparities in the South.

It's also believed that she based the character of Scout's playmate, Dill, on her childhood friend, Truman Capote. The two remained close as adults, and after the release of "To Kill a Mockingbird," Lee traveled to Kansas with Capote to research an article he was writing for the New Yorker. That article would later become his famous true-crime story, "In Cold Blood."

The book

The book was released in July 1960 and flew off the shelves, but critics had mixed reviews. Some praised it for pushing the envelope with its social commentary, while others found its characters, both black and white, to be poor representations people of the South and their lives. Although it's considered a classic, the book is still among those challenged and banned in schools and libraries, often because of language or its themes around race.

Although Lee humbly accepted the success and praise around "To Kill a Mockingbird," she's always been reclusive, avoiding the spotlight and media attention. She began work on another novel in the early 1960s, but "Mockingbird" was her only published work. Fiercely protective of the novel, she's been involved in several lawsuits regarding copyright issues and unauthorized merchandise being sold in her hometown.

The film and the future

In 1962, the novel was made into an Oscar-winning film starring Gregory Peck as Atticus Finch. Lee was pleased with the film adaptation, praising Peck's portrayal of the small-town lawyer, and called the film a work of art.

This year, Lee finally gave permission for the novel to be published as an e-book and digital audio edition e-book, saying, "I am amazed and humbled that 'Mockingbird' has survived this long. This is 'Mockingbird' for a new generation."