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.