What is meant by text complexity is a measurement of how challenging a particular text is to read. There are a myriad of different ways of explaining what makes text challenging to read, from the sophistication of the vocabulary employed to the length of its sentences to even measurements of how the text as a whole coheres. Research shows that no matter what combination of factors is considered when defining text complexity, the ability to read complex text is the single greatest predictor of success in college. This finding is true regardless of gender, race, or socio-economic status. The implication is that teaching that focused solely on critical thinking would be insufficient: it turns out that being able to proficiently read complex text is the critical factor in actually understanding complex text. A key requirement of the Anchor Reading Standard 10 in the Common Core State Standards (CCSS) is that all students must be exposed to texts of steadily increasing complexity. The system for determining text complexity involves several factors, but the increased expectations regarding the ability of students to read complex text is illustrated by a comparison of past and present Lexile Ranges. The key elements of text complexity are: (1) Quantitative factors; (2) Qualitative factors; and (3) Reader and task factors.