Ultimate Kylie is the second major greatest hits album by Australian singer Kylie Minogue, and her first greatest hits released under her contract with Parlophone, her record company between 1999 and 2015. The compilation was released in many different formats including a two-disc edition and a deluxe double disc with a bonus DVD. A separate compilation DVD with the same name, was released to accompany the audio versions. The album includes two new tracks; its lead single, "I Believe in You", and the second single, "Giving You Up". A third track, "Made of Glass", was recorded for the album but not used; it was included on the physical releases of "Giving You Up".

Ultimate Kylie was commended by contemporary critics who noted the musical and credible progression from the start of her career; some critics criticised the earlier material. The album reached the top ten in the United Kingdom, Australia, Ireland, Greece, and Germany, while it charted in several other territories including Spain, Sweden, and New Zealand. The album was certified platinum by the International Federation of the Phonographic Industry (IFPI) for one million shipments throughout Europe. "I Believe in You" debuted inside the top ten in several countries worldwide, while "Giving You Up" charted moderately in some regions. The compilation was promoted through the Showgirl: The Greatest Hits Tour in 2005. After Minogue was diagnosed with breast cancer, she cancelled the tour and was resumed with another leg in 2006.

This compilation was superseded by 2019's Step Back in Time: The Definitive Collection with only "Giving You Up" not being included on the expanded, 3-CD version of the latter.

Ultimate Kylie is Minogue's ninth greatest hits album, and her first compilation through Parlophone. The release follows her eight previous greatest hits albums, The Kylie Collection (1988), Greatest Hits (1992), Hits+ (2000), Confide in Me (2001), Greatest Hits 87–97 and its re-release (2002 and 03), Greatest Hits: 87–99 (2003), and Artist Collection (2004). Greatest Hits and Hits+ are her only compilations released through her signed labels; Greatest Hits was released through her 1987–1992 record label, PWL, and Hits+ was released through her 1993–1998 record label, Deconstruction Records. Ultimate Kylie is her first greatest hits album under her contract with Parlophone; her final greatest hits release through the contract was The Albums 2000–2010 (2011). On Minogue's website, she shared her thoughts on the release:

Since my first hit, I can’t believe how quickly time has passed. This collection is very dear to me and holds a lifetime of memories. There is nothing like time to give you a sense of perspective and I hope the listener gets as much enjoyment out of these tracks as I do. I feel lucky to have had the opportunity to experiment throughout the years and that my fans have embraced the need in me to try new approaches. I am just as excited about the new tracks featured here as I am about all the others on the record. At this point in my career, I am happy to celebrate the past and look forward to the future.

On 22 November 2004, Ultimate Kylie was released as a standard two-disc set. Three versions were issued; the standard two-disc set, and a digital release through Amazon.com and iTunes Store; as of May 2011, the digital release has been removed from digital stores. The third format was a triple-disc package, with the original two-discs and a bonus DVD, including music video content; this was released in Australia through HMV stores in 2006. A DVD with the same name was simultaneously released which included several music videos of Minogue that have never appeared on a DVD before. It includes the completed video of the single "I Believe in You", but no video of "Giving You Up" was produced at the album and DVD's release. The DVD contains all the music videos with of the songs with on-screen lyrics (with the exception of "Giving You Up", which had not been filmed at the time of release). It also contains Minogue's performance at the 2002 BRIT Awards of "Can't Get Blue Monday Out of My Head" – a mix of her song "Can't Get You Out of My Head" and New Order's "Blue Monday". Early versions of the UK DVD were known to suffer from disc rot after a short period of time, where the playing surface becomes cloudy or forms a 'cracked' pattern. The record label offered free replacements to those who returned their damaged copies. "Can't Get You Out of My Head" is also featured in edited form with the first chorus removed. "Giving You Up" had not been filmed yet and is represented in the instrumental intro on the menu page.

On 28 October 2006, upon resuming her Showgirl tour, the compilation was re-issued as the "Showgirl Homecoming Special Edition" and included the two-disc compilation plus the corresponding DVD in a three-disc set.

Ultimate Kylie received a generally positive response from music critics. PopMatters gave it a positive review, saying: "Ultimate Kylie, which seems condensed even at its double-disc length, is one of the best collections of dance music available, even while including her '80s pop hits. It is enough to get her MP3s permanently out of my "guilty pleasures" bin" and gave the album an 8 out of 10 rating, which means that the album was of excellent status and "among the best work of the given artist, or among the best in the given genre". Stephen Thomas Erlewine from AllMusic gave it a very positive review, awarding it four and a half out of five stars. At first he said "There certainly hasn't been a shortage of Kylie Minogue hits compilations", but finished the album with a positive review and ending saying "it nevertheless gives all the hits, both big and small, in one place, which means that this not only makes this ideal for fans for all levels of dedication, it means that Ultimate Kylie lives up to its billing." Music Week staff noted that "this is a "greatest hits" truly deserving of the name, and offers more hits than you can shake a stick at".