FIDH and the Human Rights Center Viasna, its member organisation in Belarus, conducted an international investigation mission in Belarus in June 2014. The mission focused on numerous cases of groundless and illegal (i.e. not connected to any violation of the law) detention and subsequent arrest of citizens solely on the basis of their membership in opposition groups or other groups and movements critical of the Belarusian government. Mission participants decided to concentrate on just one type of arbitrary detention—so-called preventive arrests. Even though there are no legal definitions for this type of arbitrary detention, the practice of its application makes it possible to define it as the arbitrary detention of citizens (without legal grounds) in the period immediately preceding important political or social events (election campaigns, official visits by leaders of foreign states, planned large-scale events held by the opposition, official large-scale events organized by the authorities, etc.). The purpose of these kinds of detentions is to isolate the activists to prevent their explicit or assumed participation in public street actions, contacts with international delegations or the press, or other types of political and civil activities. (Introduction, ragment)