This Special Issue of the Journal of Industrial Microbiology and Biotechnology (JIMB) is dedicated to Prof. Arnold L. Demain (Arny). It celebrates his worldwide impact over several decades in the important field of industrial microbiology and biotechnology. Over the years, Arny’s name became synonymous with the field! His influential publications, books, reviews, and inspiring lectures have led to national and international accolades. He has mentored an international “army” of leaders (known as Arny’s Army & Friends, or AA&F), who followed his leadership in advocating the values and uses of the disciplines and technologies of industrial microbiology and biotechnology for society and the environment. Members of AA&F, many trained by Arny at MIT, later spread his message worldwide in academia and industry. Their “next generation” students, postdocs and collaborators are now at the helm of the field. Many of the invited articles in this Special Issue of JIMB are contributed by Arny’s friends and their scientific “children and grandchildren”. All are indebted to Arny for his mentorship, guidance, friendship and inspiration, and express their gratitude by their contributions to this historic volume. The topics cover many disciplines of high interest to Arny, to the Society for Industrial Microbiology and Biotechnology (SIMB), and to JIMB, including Natural Products, Metabolic Engineering, Biocatalysis, and Fermentation. Arny’s special impact on the lives of scientists is attested to by the personal reflections of Professors Satoshi Ōmura and Joan Bennett. We all wish Arny a Happy 90th Birthday!