Jesse Eisenberg as Simon James / James Simon

Mia Wasikowska as Hannah

Wallace Shawn as Mr. Papadopoulos

Yasmin Paige as Melanie

Noah Taylor as Harris

James Fox as The Colonel

Cathy Moriarty as Kiki

Phyllis Somerville as Simon's Mother

Gabrielle Downey as Strange Woman

Jon Korkes as Detective

Craig Roberts as Young Detective

Kobna Holdbrook-Smith as Guard / Doctor

Susan Blommaert as Liz

Bruce Byron as Skinhead

J. Mascis as Janitor

Tony Rohr as Rudolph

Karima Riachy as Secretary

Tim Key as Care Worker

Andrew Gruen as Man on Train

Kim Noble as Box Man / Guard 1

Morrison Thomas as Coughing Man

Sally Hawkins as Receptionist at Ball

Lloyd Woolf as Investigator

Lydia Fox as Well-Dressed Woman at Ball / Test Invigilator

Stuart Silver as Waiter / 'The Replicator' - Guard 2

Chris Morris as Workers' Services Executive

Chris O'Dowd as Nurse

Donal Cox as Priest

Kierston Wareing as James' Funeral Date

Paddy Considine as 'The Replicator' - Jack

Dirk Van Der Gert as 'The Replicator' - Head Judge

Liam Bewley as 'The Replicator' - Wise Judge

Gemma Chan as 'The Replicator' - Glamourous Judge

Nathalie Cox as 'The Replicator' - Jack's Wife

Daniel Chapple as Executive Worker (uncredited)

Martin Crossingham as Paramedic (uncredited)

Danny as Singer (uncredited)

Catherine Delaloye as Air Hostess (uncredited)

Lukas DiSparrow as Resident (uncredited)

Joanna Finata as Bar Girl (uncredited)

Jeanie Gold as Waitress (uncredited)

Steve Saunders as Moaning Man on Trolley (uncredited)

Rade Šerbedžija as Frightening Old Man (uncredited)

Natalia Warner as The Girl (uncredited)