A practice note discussing Council Directive (EU) 2018/822 of 25 May 2018 ("EU DOTAS" or "DAC 6"), which entered into force on 25 June 2018, introducing mandatory disclosure rules for intermediaries (and in some cases, taxpayers) in respect of cross-border arrangements that exhibit specified "hallmarks". The note focuses on the UK's implementation of this Directive (including its post-Brexit transition period restriction of disclosure of cross-border arrangements to those arrangements that exhibit hallmarks concerning automatic exchange of information and beneficial ownership) and notes its replacement (from 28 March 2023) with rules implementing the OECD's model mandatory disclosure rules.