This work is one of the first attempts to make a detailed and comparative analysis of the supplementary material of several bilingual English-Spanish dictionaries from the 20th and 21st centuries. It examines the historical development of prefaces and appendices in the most representative bilingual English-Spanish dictionaries that have contributed to the development of Spanish Lexicography. Twenty-eight different editions from ten dictionaries found in important higher education institutions in the United States of America were selected for the study, and were later classified into two different categories according to their size and format. This qualitative study provides a historical overview of each dictionary and a thematic analysis by using modern postulates and guidelines proposed by well-known researchers in this discipline to standardize the review of bilingual dictionaries. The results show that most of the modern dictionaries have improved several aspects of the presentation and organization of their front, middle, and back matter. However, most of the newer editions of several dictionaries still have not implemented changes to improve the cross-reference system to relate the outside matter with the body of the dictionary. A few of these dictionaries are sold as an improved edition when the only changes are on the book cover. This study will help dictionary users in the United States identify good dictionaries. It will also be a reference for lexicographers seeking to improve bilingual dictionaries by making the presentation and organization of the outside matter more practical and more accessible for their users. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]