Police from the European Union (EU) Member States make significant use of bilateral liaison officers to cooperate with police in other countries. In the past decades, a number of TREVI and EU Council policy instruments have aimed to enhance the common use of liaison officers by the Member States. This research article discusses these policy instruments from the perspective of the practicalities of the work of liaison officers, examines the underlying rationalities of the instruments and assesses their effects. The findings show that national interests of Member States remain paramount in posting liaison officers. Practices of liaison officers are largely governed by national regulations and organisational particulars, but also depend on the high level of discretion that liaison officers can exercise. In contrast, the policy instruments are largely driven by a political rationality and little intended effect of these instruments can be detected
