Background: This review will encompass a comprehensive examination of insulin and insulin resistance, spanning its historical background, synthesis, functions, interactions, and related clinical symptoms. Within this section, we will delve into the underlying mechanisms and various scenarios, both physiological and pathological, that contribute to insulin resistance. The prevalence of insulin resistance among adults worldwide ranges from 15.5% to 46.5%. Excessive visceral fat is considered the main cause of insulin resistance. One of the tyrosine kinase receptors belonging to the Class II (Cysteine) family is the insulin receptor (IR). Adipose tissue functions as an endocrine organ, exerting influence over both glucose and lipid metabolism through the release of adipokines, pro-inflammatory factors. The transport of glucose into the interior of adipocytes relies on insulin and is facilitated by GLUT4 transporters. Adipose tissue is estimated to contribute approximately 10% of the overall glucose uptake stimulated by insulin throughout the body. The primary emphasis will be on scrutinizing insulin's functions and how insulin resistance manifests in specific bodily organs and tissues. We will also scrutinize factors like physiological, environmental, and pharmacological influences on insulin activity, along with clinical conditions associated with insulin resistance.