Ascaris lumbricoides (Round Worm) is the most common human helminth with a world wide distribution. Incidence of ascariasis remain very high in the tropical and sub tropical countries with poor sanitation, personal hygiene, and rural areas where defaecation in open place is still a common practice. Ascariasis is classified as a neglected tropical disease. Infections have no symptoms in more than 85 percent of cases specially if the number of cases are small. Pathogenecity and clinical features are either due to migrating larvae or due to adult worms. Larval migration may lead to allergic reactions, ascaris pneumonia. Adult worms are often responsible for nutritional deficiencies, toxic effects due to hypersensitivity &mechanical effects leading to intestinal obstruction. Ectopic ascariasis can lead to acute biliary obstruction, cholangitis, acute pancreatitis, acute obstructive appendicitis and peritonitis due to perforation of an intestinal ulcer or break down of a post operative suture line. Medical therapy with Albendazole is the first line drug ascariasis can be eliminated by preventing faecal contamination of soil. Advancement in recombinant protein technology may provide first step in discovery of Ascaris vaccine as well as pan helminthic Vaccine. This chapter is a updated review of ascariasis.