Under My Skin is the second studio album by Canadian singer-songwriter Avril Lavigne, released worldwide on May 25, 2004; It was her last album with Arista Records. Under My Skin debuted at number-one on the Billboard 200 albums chart and according to Billboard magazine, was ranked number 149 on the list of top-selling album of the 2000s. It has sold more than 10 million copies worldwide, three millions of which were sold in the USA, ranking the album #148 on the Billboard 200 Decade End Chart.
Having no plans of working with producers or professional writers, Lavigne wrote much of the album with Canadian singer-songwriter Chantal Kreviazuk, with whom she had developed a friendship in the summer of 2003. Kreviazuk, whose husband Raine Maida's band Our Lady Peace opened for Lavigne's concert in Europe, introduced herself at an after-party for the SARS benefit concerts held in Toronto in June 2003.
The following day, Lavigne and Kreviazuk ate lunch together, during when Lavigne shared how she wanted the development of the album to be. They wrote songs for almost three weeks at Maida's warehouse in Toronto. Kreviazuk invited Lavigne to continue working in a Malibu, California house she shared with Maida, which contained a recording studio. Many of the tracks in the album were recorded in Malibu.