IU released her sixth Korean extended-play and first cover album, A Flower Bookmark, on May 16, 2014. The album contains seven renditions of tracks that hailed from the 1980s and 1990s with a mixture of genres that included ballad, dance, folk and rock. The album came about at the request of fans and due to the positive feedback she had previously received for her cover songs. Three tracks debuted in the top ten of the Gaon Digital Chart on the week of release, with the main single, "My Old Story" (나의 옛날 이야기), ultimately peaking at number 2. However, it was her collaboration with Kim Chang-wan on the remake of his 1984 song, "The Meaning of You" (너의 의미), that became the best-selling track from the album and also her best-selling single of 2014. It was also well received critically.

IU's wish to conduct a more intimate and smaller scale concert was fulfilled in her third solo Korean concert series, "Just One Step... That Much More". The concert series took place over eight nights from May 22 to June 1 at Sogang University's Mary Hall, which had a capacity of 450 people. Tickets to all eight shows were sold out within 10 minutes of release on May 7, 2014. Profits made from the concerts were donated to the victims of the Sewol Ferry Disaster.

Two months after her solo concerts ended, IU made her debut performance in the United States at the KCON music festival held in Los Angeles on August 9–10. In their review, Los Angeles Times opined that IU had a "sprightly stage presence, and as a solo female singer, she's breaking the molds for K-pop stardom."

Throughout 2014, IU's collaborations with other artists spawned top-ten hits: "Not Spring, Love, or Cherry Blossoms" (봄, 사랑, 벚꽃 말고), the debut single of High4, which featured IU as lyricist and vocalist, reached number one on both the Gaon Digital Chart and Billboard Korea K-pop Hot 100; "Anxious Heart" (애타는 마음), recorded by Ulala Session and IU in 2012 but released more than a year later out of respect for the death of Ulala Session's lead vocalist, peaked at number four on the Gaon Digital Chart; "Sing for Me" (노래 불러줘요), which was released as part of g.o.d's eighth studio album, peaked at number nine on the Gaon Digital Chart; "Sogyeokdong" (소격동), written by Seo Taiji for his Quiet Night album and sung by IU in the October 2 release version, debuted at number four on the Gaon Digital Chart; and "When Would It Be" (언제쯤이면), a duet with her labelmate Yoon Hyun-sang for his debut album, Pianoforte, also peaked at number nine on the Gaon Digital Chart. After "Not Spring, Love, or Cherry Blossoms" topped Billboard Korea K-pop Hot 100 chart, IU became its "all-time chart leader" with five number-one songs and the artist who has spent the most weeks at number one since the chart's creation in September 2011.