After Meyer finished writing Twilight, she found herself writing multiple, hundred-page epilogues, and has said, "I quickly realized I wasn't ready to stop writing about Bella and Edward." She began writing a sequel, which was entitled Forever Dawn and skipped over Bella's final year of high school. While Meyer was still writing Forever Dawn, she learned that Twilight was going to be published and marketed as a young-adult novel. Wanting the next book to be aimed at a similar audience, she decided to write a new sequel, New Moon, which took place during Bella's senior year of high school. Therefore, Meyer started writing the outline of the book and thinking of what her characters would do, and claims that she "swiftly regretted asking them for the story." She didn't like the idea of Edward leaving at first and tried to think of other plot options, but, in the end, she said that "she accepted the inevitability of it."
Meyer wrote New Moon in five months. She found the editing process "much longer and more difficult than the same process with Twilight." Also, unlike Twilight, which Meyer intended not to publish at first, she recognized that New Moon was going to be published and had what she described as a "horrible feeling much like stage fright" while writing. However, Meyer considers Jacob to be her favorite gift the book gave, as she liked the character a lot and wanted to expand his role and presence.
The confrontation with the Volturi in the clock tower at the end of the book was the first scene Meyer wrote. She did not want to use a real city as the location for the Volturi's residence, as she did with Forks. She decided to name her city "Volturin" and chose a location in Tuscany, Italy because it matched her vision of the city being "very old and relatively remote." However, when consulting a map, she found that there was a city called Volterra in the area where she had planned to place her imaginary city. Therefore, she chose Volterra and called it "a pretty creepy coincidence."
The first draft of New Moon differed significantly from the manuscript published. Originally, Bella never found out that Jacob was a werewolf, and as a result, the seventy pages following Bella's discovery of Jacob's nature were missing. The epilogue was also different in title and content. Meyer found it difficult to write Bella's pain over Edward's departure and often cried while writing those parts. She mentioned that she never suffered a heartbreak like Bella's, so she couldn't draw inspiration for her pain from personal experiences, but based it on how she thought she would feel if she lost a child, while insisting that it came from her character, who is "much more open—to both pain and joy." She claims that "the way she chose to cope with it" was unexpected.
According to Meyer, the story was inspired by Shakespeare's Romeo and Juliet.