This category comes with an enthusiastic recommendation for one of the best texts in the OER realm: Abstract Algebra: Theory and Applications by Tom Judson, mentioned earlier. Judson’s text is not just of the highest caliber among the OER literature; the quality of this work actually surpasses the quality of most traditionally published textbooks on the subject. Judson’s text is another OER offspring of the PreTeXt project showcased above, and it is on par with Beezer’s text (mentioned above). These two texts truly are the exemplars of all other OER mathematical texts. Beyond being extremely well written, well organized, and visually pleasing, Judson’s companion home page comes equipped with Sage exercises and multiple formats—including pdf, print, online, and a newly released Spanish edition. The freedom to translate OER texts into any language for which there is sufficient interest is another benefit of open licensing. Other highly recommended textbooks in this category are A Computational Introduction to Number Theory and Algebra by Victor Shoup, Elementary Number Theory: Primes, Congruences, and Secrets by William Stein, and Algebra: Abstract and Concrete by Frederick M. Goodman.