Dyslexia is a specific learning disability that affects word-level reading and spelling, in accuracy, speed, or both. Definitions of dyslexia vary and are actively evolving, but there is broad agreement on several points: dyslexia is neurological, present from early development, persistent across the lifespan, and not related to intelligence. Dyslexia occurs across the full range of intellectual abilities. At its core, dyslexia involves difficulty learning to decode (read) and encode (spell) print.

The most established mechanism is a difference in phonological processing: how the brain works with the sound structure of language. This makes it harder to map sounds onto letters, decode unfamiliar words, and build the automatic fluency most people develop without conscious effort. Phonological processing is the most common factor, but not the only one. Working memory, processing speed, and visual word recognition can all contribute.

Dyslexia is best understood as a continuum, not a distinct category. It co-occurs with ADHD in an estimated 25-40% of cases and is increasingly recognized alongside autism, though it can be overlooked when attributed to an existing diagnosis. Many dyslexic adults describe working harder than everyone around them just to keep up, and internalizing that gap as personal failure rather than a neurological difference.