Casablancas' musical influences are varied and wide ranging, including but not limited to The Velvet Underground, The Pogues, Bob Marley, Built to Spill, Guided by Voices, The Magnetic Fields, The Ramones, and The Doors. More recently he has stated that possibly two of his favorite songs of all time are Queen's "Bohemian Rhapsody" and Bill Withers's "Lean on Me."

As The Strokes' principal songwriter, he has the greatest impact on their sound and has been known to be extremely meticulous with it. So meticulous that he was announced as one of the judges for the 2007 International Songwriting Competition. Recently, however, the band purports that Casablancas has become more communicative and more open to others' contributions.

Another recent change has come in the recording of his vocals, which is significantly clearer and louder than their first two albums. However Casablancas says this was adjusted only because it fit the songs more, and not because he was any less self-critical about his voice.

Known to not play much in Strokes' recordings, Julian has proved himself an able multi-instrumentalist through guest appearances. He's played guitar on "Sick, Sick, Sick" by Queens of the Stone Age, bass guitar on Albert Hammond, Jr.'s "Scared," and the second set of drums on the Strokes' "Evening Sun."

He has also served as inspiration for several other musicians. For instance, Courtney Love's song "But Julian, I'm A Little Bit Older Than You", from her debut solo album America's Sweetheart (2004), was written about Julian Casablancas.