AbstractThis chapter describes the principal mechanisms of resistance that allow arthropods to escape control, as discovered through laboratory toxicological and molecular genetic studies. By reviewing the scientific literature of the last 10 years, the complexities of mechanisms of resistance are discussed, including acetylcholinesterase insensitivity, the kdr factor (knockdown resistance due to altered sodium channels), enhanced metabolism, reduced penetration, and target site insensitivity, among others. The molecular biology of the resistance is also briefly described.