This special issue of ACAS II Bulletin focuses on a forthcoming change to TCAS II, the introduction of the new version 7.1. A regulatory decision (European Commission Implementing Rule) regarding implementation was published on 20 December 2011: all existing TCAS II version 7.0 installations must be upgraded before 1 December 2015 and new aircraft must be equipped with version 7.1 from 1 March 2012 to operate in European airspace. The EU Implementing Rule sets an earlier equipage requirements than those published in ICAO Annex 10 (1 January 2014 new installations, 1 January 2017 existing units).