Many parasitic helminths of veterinary importance have genetic features that favor the development of anthelmintic resistance, and this becoming a major worldwide constraint in livestock production. The principal mode of control of GI nematodes is based on anthelmintics because it is simple, cheap, and offers both therapeutic and prophylactic cover against GIT helminths. Anthelmintic resistance (AR) is said to have developed when an anthelmintic drug fails to kill the exposed population of parasites using the dose that is recommended therapeutically. In Ethiopia, the problem of Anthelmintic resistance is serious and reported frequently from different parts of the country and the rural people are not aware of this anthelmintic resistance problem. Therefore this paper is aimed to review and give background information on Anthelmintic resistance. Using a combination of drugs with different modes of action will help in delaying AR development. Resistance in worms can be the result of a variety of mechanisms and can be roughly categorized as genetic changes in the drug target, changes in the drug transport, or changes in the metabolism of the drug within the parasite. There are various in vivo and in vitro methods available to assess the efficacy of anthelmintics. Different management strategies are used to prevent infestation and/or keep infestation pressure low.