Sleeping by the Mississippi has been ranked with the great representations of the United States, including Walker Evans’ pictures of the depression, Robert Frank’s harsh vision of the 1950s and, more recently, the colour work of Joel Sternfeld. As Alec Soth’s seminal work goes on show in London and is given a handsome reprint by MACK, we revisit an interview with him from back in 2004 – when the series first came out.