Executive summaryOn 29 December 2020, the Spanish Parliament approved final legislation to implement the European Union (EU) Directive on the mandatory disclosure and exchange of cross-border tax arrangements (referred to as DAC6 or the Directive). Under DAC6, taxpayers and intermediaries are required to report cross-border reportable arrangements from 1 July 2020. However, reports will retrospectively cover arrangements where the first step is implemented between 25 June 2018 and 1 July 2020.1The Spanish legislation was published in the State Official Gazette on 30 December 2020 and entered into force on 31 December 2020, being effective from that same date.The final Spanish Mandatory Disclosure Rules (MDR)...