Professor Yoichiro Nambu passed away on 5 July 2015. As a member of the advisory board for Progress of Theoretical and Experimental Physics (PTEP), Professor Nambu helped to guide the journal in its fledgling years with his warm personality. He also inspired many researchers in Japan and around the world with his ingenious scientific achievements and valuable advice. Professor Nambu has contributed to many aspects of science and has had a tremendous influence on researchers worldwide. Some of his works have been published in Progress of Theoretical Physics, and continue to have a strong impact to this day. In 2008 he received the Nobel Prize in Physics for his outstanding contribution to the concept of spontaneous breaking of symmetry.
Researchers in Japan and around the world were deeply saddened by the loss of Professor Nambu, and a series of symposia have been held in his honor. The first of these was entitled “Great achievements of Professor Nambu to be learned by students and researchers” and was held on 29 September 2015 at Osaka City University, where Professor Nambu led the newly established theoretical physics group until his departure to the United States. The symposium was attended by an audience representing a broad spectrum of the scientific community, and they enjoyed a variety of engaging talks which reflected the great versatility and profundity of Professor Nambu's research. This special section dedicated to Professor Nambu is a collection of invited articles by the speakers at the symposium held at Osaka City University.