Helminths modulate both the adaptive and innate arms of human immune system. Such immune alteration seems to have an anti-inflammatory effect. Chronic helminth infections switch the immune response from Th1 to Th2 by various mechanisms and by different helminth derived molecules. Though these immunological responses provide a survival advantage, they seem to hamper the response to non-helminth derived antigens. Immune response to oral vaccines and many auto-immune disorders are influenced by immunomodulatory effects of helminths. As a part of eukaryotic community in the gut, helminths might have a potential role in the development of immune system.