Tell All Your Friends is the debut studio album by American rock band Taking Back Sunday, released on March 26, 2002, through Victory Records. Forming in 1999, the group underwent several lineup changes before settling on vocalist Adam Lazzara, guitarist and vocalist John Nolan, guitarist Eddie Reyes, bassist Shaun Cooper, and drummer Mark O'Connell. Taking Back Sunday released a five-song demo in early 2001, after which they toured the United States for most of the year. They rented a room in Lindenhurst, New York, where they wrote and demoed songs. In December 2001, the band signed with Victory Records; they began recording their debut album with producer Sal Villanueva at Big Blue Meenie Recording Studio in New Jersey.

"Great Romances of the 20th Century" was released as the lead single from Tell All Your Friends in March 2002. A few months later, Taking Back Sunday toured across the United States with Brand New and Rufio. At the end of the year, a Fight Club-inspired music video was released for "Cute Without the 'E' (Cut from the Team)". The group spent the early part of 2003 touring with the Used and the Blood Brothers before headlining their own tour. After that, Nolan and Cooper left Taking Back Sunday and were replaced by Fred Mascherino and Matt Rubano. In September 2003, "You're So Last Summer" was released as the album's second single, and the band began co-headlining a tour with Saves the Day, which lasted until November 2003. By that point, a music video had been released for "You're So Last Summer".

Critics have given Tell All Your Friends mostly positive reviews, highlighting its mix of musical styles. It sold 2,000 copies in the first week after its release, charting at number 183 on the Billboard 200 chart. The album was certified gold by the Recording Industry Association of America (RIAA) in the US and had sold 790,000 copies as of 2009; in 2023, it was certified platinum. It is Victory Records' longest-running release on the Billboard Heatseekers Albums chart at 68 weeks, and on the Independent Albums chart at 78 weeks. In 2012, the band toured to celebrate the 10th anniversary of Tell All Your Friends, playing an acoustic set on the anniversary tour, which was later released in 2013 as the live album TAYF10 Acoustic. It has been included on lists of the best emo albums of all time by publications such as Alternative Press, NME, and Rolling Stone.