Graded readers can be an optimal resource to help language students improve and personalize their learning experience. An extensive reading library with graded readers and well-defined levels of reading difficulty increases language students' chances of having a successful reading experience and become independent readers. However, when it comes to implementing such a library, there is a practical issue. A review of the graded readers available in Spanish reveals different proficiency levels and a lack of a uniform set of criteria for establishing levels of reading difficulty. Through the analysis of 203 titles by 12 publishers (from Spain, England, Italy, and the United States) complemented by an objective and uniform tool--a readability test--the present study validates and suggests alignment among reading levels across publishers. The ultimate goal of this study is to provide language teachers and program administrators with a uniform system of cataloging graded readers under the premise that a well-established library fosters independent language learning.