This chapter describes youth offending and youth justice: that is, offending behaviour committed by children and young people and how they are treated in the Youth Justice System. Society’s assumptions about what it means to be a child and what should be expected of children and young people in terms of their development and behaviour shape its views on and responses to youth offending. The chapter then looks at how the concepts of ‘childhood’ and ‘youth’ have been seen, theorised, and socially constructed over time, before moving on to consider explanations for youth offending and ‘delinquency’. Youth offending has tended to be explained in individualised terms, through developmental and psychological explanations. The chapter also evaluates the main formal responses to youth offending and assesses more progressive, contemporary approaches to youth offending and delivering youth justice.