Garland aims at surveying the most decisive social theories about punishment, and 'the book is thus an argument for (italics) the social approach to punishment as well as an exposition of it.' (p. 1)
As a consequence, Garland goes through Durkheim's, Rusche's, Kircheimer's, Marx-inspired, and Foucault's theories among others with providing deep analyses of their argumentation, and no less deep criticism of their reasoning, to further the discussion.
Interesting read to know about the different theories and move on with further questions to investigate.