The purpose of this paper is to present a developmental model of reading that encompasses changes across the lifespan. The author contends that until we adopt this lifelong perspective, we continue to run the risk of turning out undeveloped, unmotivated, and uncritical readers unable to fulfill their responsibilities within a democratic society. This framework of lifespan development in reading is grounded in the extensive research in expertise, particularly the research on the Model of Domain Learning (Alexander, 1997). Based on that research, the author describes several characteristics of lifespan reading development: (1) Readers' knowledge of language and knowledge of content domains are critical forces in developing competence; (2) Readers' personal interest in reading becomes a driving force in their development as competence is achieved; (3) Lifespan development involves systematic changes in readers' strategic processing; (4) Reading development is a lifelong journey that unfolds in multiple stages; (5) Profiles of successful and struggling readers are reflective of developmental forces; and (6) Readers in acclimation are especially vulnerable and in need of appropriate scaffolding. The unique configuration of knowledge, interest, and strategic processing for each of the stages of lifespan reading development--acclimation, competence, and proficiency/expertise--is discussed. Further, educational implications and instructional recommendations for these stages and the varying profiles of more or less successful readers are considered.