Pesticide resistance has become one of the pressing problems of ecology and agriculture because it makes it difficult to deal with pests and ectoparasites while increasing the chemical load on the environment. This paper focuses on the importance of studying insecticidal resistance in agricultural, veterinary, and medical insects. Brief information is given concerning the resistance of ectoparasites and crop insect pests in different world regions to commonly used insecticides. The main approaches for identifying insecticide resistance in field insect populations are listed. The progress achieved in understanding the molecular basis of insecticidal resistance in insects is briefly described, and the primary areas of recent research are outlined. The importance of assessing the resistance profile and the potential for insecticide resistance developing in field insect populations are emphasized. The study of molecular mechanisms of insecticidal resistance to specific compounds is important for searching for new active agents and developing strategies for their application.