21 werd grotendeels opgenomen in Malibu met de legendarische producer Rick Rubin (bekend van Johnny Cash, Jay Z en Red Hot Chilli Peppers) en gedeeltelijk in Londen met producer Paul Epworth (Bloc Party en Florence And The Machine). Voor de totstandkoming van 21 werd Adele vooral geïnspireerd door artiesten als Wanda Jackson, Yvonne Fair, Andrew Bird, Elbow, Mary J Blige, Mos Def, Tom Waits en Kanye West. Het album wordt voorafgegaan door de single Rolling In The Deep. Dit nummer werd geschreven en geproduceerd door Adele en Paul Epworth. "It's a dark bluesy gospel disco tune," aldus Adele over de single.<br /><br />Over het album zegt ze: "I'm very excited, nervous, eager, anxious but chuffed to announce my new album! It's taken a while and it knocked me for six when writing it. It's different from "19", it's about the same things but in a different light. I deal with things differently now. I'm more patient, more honest, more forgiving and more aware of my own flaws, habits and principles. Something that comes with age I think. So fittingly this record is called "21". The whole reason I called my first album "19" was about cataloging what happened to me then and who I was then, like a photo album you see the progression and changes in a person throughout the years".