Seriousness and proportionality are key concepts in the ‘just deserts’ approach to sentencing which was endorsed by the Criminal Justice Act 1991. This chapter analyses the extent to which this framework based on retributivist principles has been undermined by subsequent changes in legislation. It examines law and guidance on constructing seriousness, particularly in relation to harm and culpability, and on determining a commensurate sentence. Throughout it refers to the Sentencing Code (referring to the Sentencing Act 2020 when we are explaining how changes occurred) and illustrates issues by using examples from recent guidelines, focusing discussion on custodial sentencing. Finally, it discusses criticisms of modern retributivism from a range of standpoints, including Marxian perspectives.