Language and literacy are cognitive skills of exceptional complexity. It is therefore not surprising that they are at risk of impairment either during development or as a result of damage (e.g. stroke) later in life. Impaired language and literacy can arise from a general learning impairment. However, two developmental disorders, specific language impairment (SLI) and dyslexia, which affect oral and written language, respectively, are "specific" in that they are not part of a more general learning difficulty. SLI and dyslexia each affect 5-10% of the general population, and they are the focus of the papers in this special issue.