Designed by the Language Research Institute of Seoul National University, this textbook is part of a three volume set, with 25 lessons in each volume. Each lesson is made up of Vocabulary, Pronunciation, Main Text, Grammar, and Exercise sections. The content is easy and interesting as well as educational, and reflects the phonological and grammatical characteristics of Korean. It also introduces aspects of Korean culture in a natural and unaffected way. Above all, the books enable you to study alone, without the aid of a teacher or classroom environment. Also available with audiocassettes or CDs through the publisher.
Although I enjoyed this as a reasonably fast way to review Korean, I don't recommend it generally. Korean was my mother tongue (I eventually lost most of it by going to American schools, and English is the only language I'm actually fluent in), so I was able to fall back on that knowledge to work through this book. However, this is really too fast-paced for people who are complete newcomers to the language, and there are far too few exercises to help newcomers get a grip on grammatical patterns and vocabulary. If you already know some Korean and want a fast refresher course, this is an acceptable option; otherwise, you should probably look for a more thorough textbook.