Member states holding the presidency work together closely in groups of three, called 'trios'. This system was introduced by the Lisbon Treaty in 2009. The trio sets long-term goals and prepares a common agenda determining the topics and major issues that will be addressed by the Council over an 18-month period. On the basis of this programme, each of the three countries prepares its own more detailed six-month programme.
Three MS always work together over their 18 months. This provides continuity for long-term goals. This is arranged in the Lisbon Treaty (2009).