The purpose of this article is to review empirical studies that have investigated the cognitive and language skills of adults who are functionally illiterate (A-IL), that is, individuals whose literacy skills are too low to meet the literacy demands of society, even though they have attended school and are not illiterate in the strictest sense of the term. Three questions are addressed: (1) What are the types of reading and spelling difficulties that characterize adults who are A-IL? (2) Are their written language difficulties related to cognitive or language impairments which could explain their failure to learn? (3) What are the implications of these psychological findings for adult education? Copyright © 2010 John Wiley & Sons, Ltd.