Lewis MacDougall (Conor), Sigourney Weaver (Grandma), Felicity Jones (Mum), Toby Kebbell (Dad), Ben Moor (Mr. Clark), James Melville (Harry), Oliver Steer (Sully) more..., Dominic Boyle (Anton), Jennifer Lim (Miss Kwan), Max Gabbay (Steven), Joe Curtis (Peter), Morgan Symes (Lawyer), Max Golds (5-Year-Old Connor), Frida Palsson (Lily's Mum), Wanda Opalinska (Female Nurse), Patrick Taggart (Teacher), Lily-Rose Aslandogdu (Lily), Liam Neeson (The Monster (voice)), Geraldine Chaplin (The Head Teacher (uncredited)), Jake Talbot (Rollercoaster Boy (uncredited)), Lee Bolton (Rollercoster Rider (uncredited)), Garry Marriott (Paramedic (uncredited))

Patrick Ness (Screenplay), Patrick Ness (Novel), Siobhan Dowd (Idea), Belén Atienza (Producer), Sandra Hermida (Co-Producer), Sarah Wheale (Line Producer), Fernando Velázquez (Original Music Composer) more..., Óscar Faura (Director of Photography), Jaume Martí (Editor), Bernat Vilaplana (Editor), Shaheen Baig (Casting), Eugenio Caballero (Production Design), Jaime Anduiza (Art Direction), Ravi Bansal (Art Direction), Dídac Bono (Art Direction), Pilar Revuelta (Set Decoration), Stephen Noble (Costume Design), Álvaro Augustín (Executive Producer), Ghislain Barrois (Executive Producer), Sandra Hermida (Executive Producer), Mitch Horwits (Executive Producer), Jonathan King (Executive Producer), Enrique López Lavigne (Executive Producer), Patrick Ness (Executive Producer), Bill Pohlad (Executive Producer), Jeff Skoll (Executive Producer), Patrick Wachsberger (Executive Producer), Tom Holland (Stand In), Steve Joberns (Thanks), Oriol Tarragó (Sound Designer), Marese Langan (Makeup Designer), Marese Langan (Hair Designer), Félix Bergés (Visual Effects Supervisor), Pau Costa (Special Effects Supervisor), David Martí (Makeup Effects), Montse Ribé (Makeup Effects), Jaume Martí (Post Production Supervisor), Albert Carreras (Camera Operator), Eugenio Mira (Second Unit Director), José Luis Rodríguez (Gaffer) and others.