One is the debut studio album by Britishprogressive 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 Perspective EP.