Introduction The Tachinidae contains more than 8000 species (Ziegler, 1998). All species of Tachinidae are parasitoids of other arthropods, primarily insects (Stireman et al., 2006). The most common hosts of tachinids are larval Lepidoptera that feed on foliage. They also attack a range of other insects, especially Heteroptera (nymphs and adults), Coleoptera (larvae and adults), and Hymenoptera (Symphyta larvae) (Wood, 1987). However, the hosts of most tachinid species are still unknown. Detailed information on West Palearctic hosts can be found in the works of Herting (1960), Tschorsnig and Herting (1994), and Kara and Tschorsnig (2003). The aim of this research was to determine the tachinid parasitoids reared from lepidopterous and heteropterous hosts in the regions belonging to Kelkit Valley of Amasya, Sivas, and Tokat provinces. This manuscript is a result of the PhD thesis of the first author (Atay, 2011). 2. Materials and methods This study was performed in the regions belonging to Kelkit Valley of Amasya, Sivas, and Tokat provinces from 2008 to 2011. The adults and larvae of the potential hosts were collected from crop, forest, weed, and ornamental plants during the vegetative period. They were brought to the laboratory with their food-plants for rearing. They were transferred to separate cages (30 × 60 cm in size, with 5-7 cm of moist soil), kept at 25 ± 2 °C and 60%-70% relative humidity, and checked daily. Adult tachinids and hosts (not parasitized by tachinids) were killed, pinned, and prepared for identification. The tachinids were identified by the authors using the keys of Tschorsnig and Herting (1994) and Tschorsnig and Richter (1998). Determination of some tachinid species and confirmation of tachinid/host-couple records were carried out by Dr HP Tschorsnig (Staatliches Museum für Naturkunde, Stuttgart, Germany). Nomenclature and arrangement of tachinids follow Herting and Dely-Draskovits (1993) while nomenclature of lepidopterous and heteropterous hosts follows Karsholt and Razowski (1996) and Berend (2011), respectively.