The inflammatory bowel diseases (IBD) are defined as nonspecific chronic intestinal inflammations with possible systemic involvement. IBD have unknown etiology. The inflammatory process is complex and heterogeneous, both as to the characterization of the disease that affects the digestive tract, without an intelligible pattern of revelation and balance, and in its different systemic damages when including the extensive and severe extraintestinal symptoms. Aparently, the natural history of the disease is irregular in relation to the offending agent system and the attacked system, both in the intestinal and extraintestinal teguments. Isolated aspects showing irregularity in this balance gives us the notion that IBD, especially Crohn's disease, can be caused by the stimulation of an immune response caused by damaging agents (intestinal bacteria), but mediated by inadequate genetic factors, whose expressions determine different individual susceptibilities. These observations have been shown in genetic studies that emphasize the importance of pathological interaction between host and bacteria subsidized by a genomic region that contains genes producing proteins (NOD2 -nucleotide-binding oligomerization domain containing 2) participating in an enhanced defense response by the tissue. Increased numbers and the activation of these cells in the intestinal mucosa elevate local levels of tumor necrosis factor α (TNF-α), interleukin-1β, interferon-γ, and cytokines of the interleukin-23-Th17 pathway. So, it can be assumed that the susceptibility, which is a result of genetic alterations, is connected to an exaggerated response in the pro-inflammatory phase because of a dysfunction in the intestinal immune system. The identification of tumor necrosis factor (TNF-α) as the active element in the pro-inflammatory inadequate response gave rise to the heightened production of biological substances that could block TNF-α, at different levels, opening a large field of view to new treatment of IBD.