Vectors play an important role in the transmission of parasites and diseases. Trypanosomosis is a disease caused by blood parasites called Trypanosoma in animals and humans which is responsible for huge economic loss particularly in Africa. The disease is commonly transmitted by insects named tse tse flies that are biological vectors of Trypanosoma. However, the disease is also transmitted by other insects called biting flies which only acts as mechanical vectors where the parasite is carried by the flies and injected into the animals without going into a biological reproduction in the flies. These flies are serving like injection needles only. In Ethiopia, around the largest lake called Lake Tana (surface area of 3,300 km²), the disease is so prevalent in domestic animals with no apparent existence of the tse tse flies.The disease causes substantial economic loss to the farmers and livestock producers. Therefore, this book deals with the investigation of the factors behind the vectors involved in transmitting this disease. It also illustrates the ecology of vectors, the prevalence of the disease & response of infected or sick animals to treatment of available drugs in the market.