One is the debut studio album by British progressive metal band Tesseract. Released on 22 March 2011, the album features six tracks. The third track, "Concealing Fate", was split into six parts for a total length of twenty seven minutes and forty seconds. This was Tesseract's only full-length release with vocalist Daniel Tompkins until his return in 2014. A bonus track entitled "Hollow" was released digitally to those who pre-ordered One from Century Media.
A live studio play through of "Concealing Fate" was also included as a bonus DVD along with the album. In September 2011, an instrumental version was released digitally and in October that year both the album and the instrumental version were released on vinyl as a double LP. "Nascent" was released as a promotional single in February 2011, and music videos were released for both "Nascent" and "Deception". Acoustic renditions of "Perfection", "April" and "Origin" were featured on the band's second EP Perspective, which released the following year.
In 2024, Loudwire elected it as one of the 11 best progressive metal debut albums.