We are honored to be Guest Editors of this special issue of Journal of Combinatorial Optimization dedicated to our friend Gerard Jennhwa Chang on the occasion of his 60th birthday. Gerard received his B.S. in mathematics from National Central University in Taiwan in 1974, and Ph.D. in operations research from Cornell University in USA in 1982. Then he returned to Taiwan and devoted himself to mathematics education and research in Taiwan. He was a faculty member at National Central University, National Chiao Tung University, and currently he is affiliated with National Taiwan University.

Gerard has made significant contributions to research in graph theory and combinatorial optimization, as well as to the development of the discrete mathematics community in Taiwan. He has wide research interests and has published over 180 research papers in the topics of graph coloring, domination, algorithmic graph theory, group testing, etc. In addition to his research, he works tirelessly with students and young scholars, assisting them in building successful academic careers. Besides guiding students in their research, he has also helped and encouraged many students entering appropriate Ph.D. programs abroad and promoted collaborations between scholars in Taiwan and abroad, which he considers important for the development of discrete mathematics, as well as the whole mathematics, society in Taiwan. Gerard served at numerous administrative positions and is the incumbent President of the Mathematical Society of the Republic of China. Through these administration services, he helped greatly in building a friendly and stimulating research environment in mathematics, especially in the discrete mathematics community. We are in debt to him a great deal, and we wish him happy birthday and many more successful years in his academic life.