What is dyslexia? -- The definition of dyslexia -- The phonological representations hypothesis -- Learning to read and to spell -- Dyslexia : a written language disorder -- Individual differences in dyslexia -- The severity hypothesis -- Biological bases of dyslexia -- Dyslexia : a sensory impairment -- Helping to overcome dyslexia -- Proficiency and deficiency : the role of compensation -- Conclusion and future prospects.