This review article provides more information about the incidence of helminths affect the gastrointestinal tracts of poultry in different countries, life cycle, clinical picture, diagnosis, and prevention and control measures of such infections. Backyard and deep litter production systems show higher helminth infections than cage system. Moreover, the incidence of helminth infection is more common in tropical countries of Africa and Asia than of European ones due to the suitability of environment and management conditions. Nematodes and cestodes are the most common gastrointestinal helminths of avian species, followed by trematodes. The life cycles of helminths may be direct or indirect, but the infection is usually through faecal-oral route. Affected birds show general signs, low production performance parameters, and even death due to intestinal obstruction and rupture. Lesions of the infected birds reveal catarrhal to haemorrhagic enteritis according to the severity of infection. Diagnosis of affection is mainly based on post mortem examination or microscopic detection of eggs or parasites. As internal parasites adversely affect the host causing poor feed utilization and low performance, thus intervention control strategies are urgent. Prevention and control strategies are relied on application of strict biosecurity measures, eradication of intermediate hosts, early routine diagnosis, and continuous application of specific anthelmintic drugs. Deworming using herbal medicine is recent and successful and may be good alternative to chemicals. In conclusion, helminth infections of poultry remain a major hurdle against the profitable production in poultry producing countries and necessary preventive and control measures should be strictly applied by poultry producers.