Global challenges require global answers. This is especially the case with the current threat of transnational terrorism. Undoubtedly, there is an increasing need for states to cooperate in the sphere of counter terrorism. Information, even sensitive information, has to be shared because of two compelling reasons:
• to prevent attacks, or
• to investigate after an attack, as fast as possible and to ensure that attack-ers get appropriate punishment, and to nip further attacks in the bud.
But what should such cooperation actually look like? Especially after the 9/11 attacks, state institutions have tried to share information – about knowledge of terror organizations and to interlink them. Similarly, after the attacks in Madrid (2004) and London (2005), the European Union (hereafter EU) has in-tensified the coordination and interlinking of security organizations.