In 2007, the New Zealand Ministry of Education formally recognized the condition of dyslexia for the first time and has subsequently developed a working definition of the condition. The aim of this article is to draw on contemporary theory and research on reading development, reading difficulties, and reading intervention to describe what the authors believe are four key components of a definition of dyslexia/reading disability. They begin by discussing some preliminary factors that need to be considered in developing a definition of dyslexia. The authors then present the four components of their proposed definition, drawing on a framework for conceptualizing reading difficulties derived from the simple view of reading. They conclude by comparing their definition of dyslexia with the working definition put forward by the ministry. (Contains 1 figure.)