According to producer Steve Mac in an interview with HitQuarters, preparation for the album would involve Simon Cowell compiling a list of around 200 potential songs. Cowell would then whittle this number down to around 40 which he then presented to Mac for consideration. Mac would then tell Cowell which of these would or would not work. When the song list had been reduced to around 18 or 19 songs Mac would then try out the songs with the band to see which worked for them. 15 songs would then be recorded for the album.
The songs on Siempre ("Always" in Spanish) include new arrangements of "Nights in White Satin" (originally by The Moody Blues), "Caruso", "Without You", "Somewhere", "You Raise Me Up", a new version of the song "Music" from the 1970s renamed "Musica", and re-arranged by its original British composer John Miles. The album also features a cover of Bryan Adams' "Have You Ever Really Loved a Woman?" translated into the Spanish "Un Regalo Que Te Dio La Vida" (which literally means "A Gift That Life Gave You"). This album includes the Spanish adaptation by the famous Mexican composer and musician Armando Manzanero of "Una Noche" ("One Night," Spanish). Other original songs in this album include "La Vida Sin Amor" ("Life without Love," Spanish), and "Come Primavera" ("Like Spring," Italian).
The album was released on November 21, 2006 in the United States and globally on November 27, 2006.
In the United States, varying stores had the rights to different songs from their "Live at the Greek" DVD, which were used to make up an exclusive live bonus track, ensuring that an album of 11 tracks was released to the USA just like every other country would receive.