In order to combat terrorism and serious crime, law enforcement authorities have had to adapt their investigative means and develop special investigation techniques. These techniques are used to systematically gather information in such a way that they do not alert those being investigated. Since there is a risk that they may infringe individual rights, special investigation techniques must be subject to control. This has been advocated by the European Court of Human Rights which "has already recognised the need, inherent in the Convention system, for a proper balance between the defence of the institutions of democracy in the common interest and the protection of individual rights". This publication contains Recommendation Rec(2005)10 of the Committee of Ministers to member states on "special investigation techniques" in relation to serious crimes including acts of terrorism. It aims at promoting the effective use of special investigation techniques by judicial and prosecuting authorities in the framework of their criminal investigations in relation to serious crimes, including acts of terrorism, whilst ensuring strict respect for the rights and freedoms of the individual.