Reviews:

I have personally known Dr. Heiko Bittmann for many years and have watched with keen interest as he meticulously studied the history and evolution of Budo, of which Karatedo is a part. A longtime foreign resident of Japan his insights are nothing short of amazing and, in my opinion, he's a perfect example of a Scholar Warrior. Finally translating the main parts of his original German PhD dissertation on Karatedo, this work is now available in English and is hugely significant. It's certainly a MUST-HAVE for any researcher along with all followers of traditional karate serious about learning the true history of Karatedo. I highly recommend this book and any others that Dr. Bittmann may write.
Patrick McCarthy, Hanshi 8th dan (Director - International Ryukyu Karate-jutsu Research Society), "Uchinadi" Journal 2006/1

The book is well researched using Japanese sources with extensive notes, bibliography, glossary and index. An excellent insight into the origins of Japanese Karatedo, with information that cannot be obtained elsewhere in English. 
John Sparkes; Combat Arts Archive

I just want to tell all the budôkas of Okinawan and Japanese martial arts: If you are looking for a great book to enlighten your martial arts knowledge then you need to read "The Teachings of Karatedô" by Heiko Bittmann. Insights to our past! Great masters who made it: Funakoshi, Miyagi, Mabuni, Ôtsuka and more .... This book is deep in knowledge ... you cannot beat the price!  
P. H. Taylor, Hanshi 8th Dan Matsubayashiryû Karatedô; 42 plus years - November 2011

In short: Bittmann’s work is readable and well researched, as well as being an important and serious contribution, not only regarding the teachings of the Way of the Empty Hand, but also concerning the historical development and the roots of the basic principles of the Martial Arts.
Dr. Andreas Niehaus, in NOAG 167-170 (2000/2001) / Excerpt from a review of the published edition of the German doctoral thesis

For someone who wants to know about the history and tradition of Karate-Do in detail, I recommend Heiko Bittmann’s book … which deals with this theme with great competence, and covers a lot of Japanese sources.
Joachim Grupp, in "Shotokan Karate: Kata 2", Meyer and Meyer, 2003 / Excerpt from a review of the published edition of the German doctoral thesis

Description:

This book is a short version of the German doctoral thesis in the field of Japanology (1998). It presents English translations of texts on the teachings of the Way of the Empty Hand together with explanations. There have been few and in some cases no English translations of these texts until now. They include the writings of the founders or influential masters of the 'four major schools', Shôtôkan, Gôjûryû, Shitôryû and Wadôryû, Funakoshi Gichin, Miyagi Chôjun, Mabuni Kenwa and Ôtsuka Hironori respectively. However, these texts also provide insight into the fundamental way of thinking within the traditional Japanese Ways of Martial Arts as a whole. To give a background to the texts and to allow a deeper understanding of them an account of the historical development of the Japanese martial arts, an introduction to some important basic principles - such as 'Way' - dô, 'Emptiness' - kû and 'Form' - kata - and a discussion of their written transmission, including new translations of important teaching texts of Miyamoto Musashi, Yagyû Munenori and Takuan Sôhô, are also presented. Biographies of the aforementioned Karatedô masters and commentators on their texts which serve to illustrate one of the most important developmental phases in the history of Karatedô are included as well. The Appendix considers the 'respectful salutation' (rei) and its performance in connection with the Way of the Empty Hand. In addition, those interested in further study will find comprehensive notes as well as both an extensive bibliography and a glossary of terms and names with their Japanese and Chinese characters.