Tanacu is a commune located in Vaslui County within the Western Moldavia region of Romania. The administrative area of the commune is composed of two primary villages: Benești and Tanacu.
The geographical composition of the commune has changed over time due to administrative restructuring. From 1968 until 2004, the territory included the villages of Muntenii de Sus and Satu Nou; however, these were subsequently split off to form their own separate entity known as the Muntenii de Sus Commune.