From what I can tell, this is the most popular textbook for introductory Japanese. This is what we used at the University of Maryland, Yokosuka campus in 2001, and I know it is also what the Bernard Language School (Tucson, AZ) uses. It is clear, concise, and the lesson plans are logical. The vocabulary is very practical for everyday use, and many lessons revolve around the most basic functions (ordering food in a restaurant, buying tickets at the train station, etc). Book I has only hirugana and katakana. No kanji until Book II.