The Special Investigation Service or STT (Lithuanian: Specialiųjų tyrimų tarnyba) is a law enforcement institution in Lithuania serving under the Seimas and the President of Lithuania to combat corruption.

[1] With departments in Kaunas, Klaipėda, Šiauliai and Panevėžys, its objectives are to identify and investigate cases of corruption as well as to prevent it through education and introduction of improved procedures in the public sector.

With growing awareness of corruption in 1990s and several scandals (most notable of them was linked to the Prime Minister Adolfas Šleževičius), the Homeland Union won 1996 Lithuanian parliamentary election.

The newly formed Lithuanian government, led by Gediminas Vagnorius, decided in 1997[1] to establish a separate organization for addressing the problem.

Main task of the STT was detection and detention of corrupt and abusive of power officials (civil servants, judges and so).