The pace of development of the justice and home affairs (JHA) acquis has been quite impressive, especially since the Amsterdam Treaty (and the new Title IV), which has offered a new legal basis and possibilities for progress in this area. After the entry into force of the Single European Act, the balance has been moving increasingly from national towards European Union solutions in JHA. At first the process was steady, but slow. This is unsurprising given that it was the first attempt by a supranational organisation to address problems such as immigration or cooperation in criminal matters. The already voluminous JHA acquis is still evolving. Most of the text is legally binding, yet only a small part of the Treaty objectives of Title IV TEC and Title VI TEU have been implemented so far. The challenge for the enlarged EU regarding the JHA acquis is therefore a dual one (Monar 2004):
· ‘maintaining’ the acquis in the sense of preserving what has already been achieved and ensuring that it is effectively implemented; and
· ‘developing’ the acquis in the sense of making certain that the momentum is not lost.
This paper examines the key post-enlargement challenges in JHA – the problems and solutions that are incumbent to the implementation of the JHA acquis and how the lack of mutual trust can be overcome to enhance decision-making and implementation capabilities after the enlargement of 1 May 2004.