This chapter discusses tonsils and adenoids, where the palatine tonsils are a mass of lymphoid tissue lying between the palatoglossal and palatopharyngeal folds. The tonsillar bed is made up mainly of fibers of the superior constrictor except inferiorly where there may be fibers of the styloglossus pass anteriorly into the tongue. The alimentary tract contains aggregates of lymphoid tissue known as gut-associated lymphoid tissue. The mucous membrane of the tonsil is innervated by the tonsillar branch of the glossopharyngeal nerve and the lesser palatine nerves. The tonsils and adenoids are made up of lymphoid tissue arranged in follicles. Being lymphoid tissue, the adenoids and tonsils are involved in the generation of immunity in early life. Enlargement of the adenoids and tonsils in the absence of recurrent or chronic infection is virtually universal. Tonsillar size is not indicative of active infection or a previous history of repeated infections.