Based on the literature overview and summarizing of practical experience we provides a current review of data regarding the epidemiology, etiology and pathogenesis of IBD. In this review authors focuse their attention on different links of the immune system, including the components of the innate immune system (macrophages, monocytes, neutrophils, dendritic cells), adaptive or acquired immunity (T and B cells), secreted mediators (cytokines and chemokines), as well as the cells of the intestinal epithelium and congenital limphoid cells, because according to modern concepts, elements of this system are the key factors of understanding the pathogenesis of IBD.