Chapter 4 argued that in order to understand more about the nature of law in EU integration it is necessary to analyse ‘EU law in action’. ‘Law in action’ draws attention to the intersections between a ‘social’ and a ‘legal’ sphere because power relations mediate such intersections. They are also a key aspect of BAT determinations. This chapter therefore traces how a political discourse, especially expressions of interests in relation to what constitute ‘the best available techniques’, shape BAT determinations at the first level of the implementation of the IPPC Directive, the drafting of BREF documents for the whole of the EU. BREF writing generates ‘EU law in action’ in various ways. First, the fifth chapter of each BREF lists ‘BAT conclusions’. While these are not legally binding, they have to be taken into account by local permitters when they determine BAT for a specific plant. Second, participants who produce the relevant BREFs make numerous suggestions as to what should be considered as BAT during discussions in the BREF drafting process. Central to the generation of ‘BAT law in action’ is the procedure through which BAT determinations are achieved. This chapter argues that an analysis of a political discourse is key to understanding procedures for determining BAT in the BREFs. It draws attention to the productive nature of power relations by analysing how they construct procedures for determining BAT.