Dyslexia is a learning disability characterized by problems with expressive, receptive, oral or written language and affects 15% of children in the US.

Dyslexia is a specific learning disability that is neurological 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.

Adopted by the IDA Board of Directors, Nov. 12, 2002. This Definition is also used by the National Institute of Child Health and Human Development (NICHD).

More information can be found:

http://www.interdys.org/
International Dyslexia Association, formerly the Orton Dyslexia Association.
Lots of information for teachers, students, parents, etc.

http://www.SparkTop.org/explore/explore.html
"A Kids Only” website where no two brains spark alike - a place where kids who learn differently can create awesome stuff... play great games... connect with other kids... and discover new ways to succeed in school and in life."

http://www.ninds.nih.gov/health_and_medical/disorders/dyslexia_doc.htm
Information sheet compiled by the National Institute of Neurological Disorders and Stroke, National Institutes of Health

http://www.ldaamerica.org
Learning Disabilities Association of America

Interesting site, Great Britain
http://www.dyslexia-information.com