There are two main forms, ‘acquired dyslexia’ and ‘developmental dyslexia’. Acquired dyslexia is impairment that results from brain injury or disease, often in adulthood and after literacy skills have been in place. Developmental dyslexia is impairment that emerges during the course of learning to read and for which there appears to be no gross brain damage of the kind seen in the acquired form. Although some researchers have explored the similarities between the two forms (e.g. Coltheart 2005), in this chapter we focus on developmental dyslexia.