Reading comprehension is not a skill someone learns and can then apply in different reading contexts. It is one of the most complex activities that readers engage in on a regular basis, and the ability to comprehend is dependent upon a wide range of knowledge and skills. Despite a common view about comprehension, several lines of enquiry have recognized the true complexity of reading comprehension for some time. One individual may have multiple levels of comprehension ability depending upon what they are reading and why they are reading it. Chief among the factors influencing reading comprehension is background knowledge. Why is knowledge so critical for comprehension? To begin with, it provides a framework for organizing incoming information and guides the reader as a text is read through. Not only does knowledge improve comprehension, but comprehension allows the reader to build new knowledge. This article discusses comprehension as skill myth, shares a more accurate and complex model of comprehension, highlights the role of knowledge and what it does for comprehension, and provides implications for instruction and assessment.