Dyslexia is a set of processing difficulties that affect the acquisition of reading and spelling. In dyslexia, some or all aspects of literacy attainment are weak in relation to age, standard teaching and instruction, and level of other attainments. Across languages and age groups, difficulties in reading fluency and spelling are a key marker of dyslexia. The nature and developmental trajectory of dyslexia depends on multiple genetic and environmental influences. Dyslexia can affect the acquisition of other skills, such as mathematics, reading comprehension or learning another language. The most commonly observed cognitive impairment in dyslexia is a difficulty with phonological processing (i.e. in phonological awareness, phonological processing speed or phonological memory). However, phonological difficulties do not fully explain the variability that is observed. Working memory, processing speed and orthographic skills can contribute to the impact of dyslexia. Dyslexia frequently co-occurs with one or more other developmental difficulties, including developmental language disorder, dyscalculia, ADHD and developmental co-ordination disorder. For children and young people, dyslexia can affect reading accuracy and fluency, spelling, writing and, for some, reading comprehension. As educational demands increase, difficulties may become more noticeable, particularly when they are expected to read and process information quickly, produce extended written work or work under timed conditions. Identifying dyslexia can help to provide a clearer understanding of an individual's strengths and difficulties and inform appropriate support. For adults, dyslexia does not disappear, although its impact varies considerably between individuals. Adults may experience difficulties with reading speed, processing and retaining written information, spelling, written organisation or completing literacy-based tasks efficiently. These difficulties can become particularly noticeable in higher education or the workplace, where there may be greater demands on reading, writing, organisation and working under time pressure. Appropriate support may include individual strategies, reasonable adjustments and assistive technology. A diagnostic assessment can provide a clearer understanding of an individual's strengths and difficulties and make recommendations for support in education or the workplace. Want to know more about the updated definition of dyslexia? Read our blog on the 2025 Delphi definition and what it means.