At the International Dyslexia Association (IDA) conference in October, researchers and educators unveiled a new definition of dyslexia—the first revision since 2002.

In the 23 years since the original definition was adopted, our understanding of dyslexia has expanded significantly through advances in neuroscience, linguistics, and literacy research. The updated definition reflects that broader and more nuanced understanding.

Here is the original 2002 definition that guided research and educational practice for over two decades:

2002 IDA Definition of Dyslexia

Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities.

These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction.

Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.

Here is the revised definition that reflects new research and a more comprehensive understanding of how dyslexia develops and presents across individuals and languages.

2025 IDA Definition of Dyslexia

Dyslexia is a specific learning disability characterized by difficulties in word reading and/or spelling that involve accuracy, speed, or both and vary depending on the orthography. These difficulties occur along a continuum of severity and persist even with instruction that is effective for the individual's peers.

The causes of dyslexia are complex and involve combinations of genetics, neurobiological, and environmental influences that interact throughout development. Underlying difficulties with phonological and morphological processing are common but not universal, and early oral language weaknesses often foreshadow literacy challenges.

Secondary consequences include reading comprehension problems and reduced reading and writing experience that can impede growth in language, knowledge written expression, and overall academic achievement. Psychological well-being and employment opportunities may also be affected.

Although identification and targeted instruction are important at any age, language and literacy support before and during the early years of education is particularly effective.

This updated definition recognizes dyslexia as a complex and varied condition, influenced by multiple factors and expressed along a continuum rather than as a single profile. It also highlights the importance of early support and acknowledges the broader life impacts reading difficulties can have.

As research continues to evolve, so too does our understanding of how to support dyslexic learners and how to design learning environments that allow every reader to succeed.