The most effective control measure against the Asian chestnut gall wasp (ACGW), Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), the most dangerous insect pest of the chestnut worldwide, is classical biological control by using Torymus sinensis Kamijo (Hymenoptera: Torymidae), which is a larval parasitoid specific to the ACGW in its native range, China. In Turkey, this parasitoid was imported from Italy, and introduced to the affected areas in 2015 and 2016. The relevant literature constitutes a vast knowledge on T. sinensis. Additionally, a significant amount of experience has been obtained since 2014 when the pest was first recorded in Turkey. In this review, we aim to bring this knowledge and experience into Turkish, and to present them to the researchers and practitioners in Turkey. Biological control might bear some ecological risks just like natural invasion. In this review, we particularly aim to present information on the ecological risks of introducing T. sinensis to a new environment and measures to lessen these risks. Finally, we aim to designate important unknown aspects of T. sinensis biology and ecology that might have consequences for the biological control efforts in Turkey and in the world.