Gerlovo or Gerilovo (Bulgarian: Герлово, Герилово) is a small geographic and ethnographic region in Northern Bulgaria, a hilly fertile valley in the northeastern Balkan Mountains, south of the Ludogorie region. It lies between the Lisa, Preslav-Dragoevo and Kotel-Varbitsa mountains and covers much of Varbitsa municipality of Shumen Province, with smaller parts in Omurtag municipality (Targovishte Province) and Kotel municipality (Sliven Province). The main river is the Kamchiya, which runs through the entire valley and forms the Ticha Reservoir; the only sizable town is Varbitsa.