Hugh W. Catts, Charles Haynes, R Malatesha Joshi
In October 2025, the Board of Directors of the International Dyslexia Association approved a revised definition of dyslexia. This paper introduces this 2025 definition, outlines the iterative and data-driven process used in its development, and clarifies the intended purposes and boundaries of the definition for different stakeholders. The paper also reviews the current scientific evidence relevant to each component of the definition and provides the rationale for revisions to the 2002 IDA definition. In addition, it offers a set of high-level, practice-oriented guidelines intended to support the appropriate application of the definition. Finally, the paper emphasizes that, like its predecessors, the 2025 definition should be regarded as a living document, one that will continue to evolve as scientific understanding advances and as educational and clinical practices change.