[Preface for special issue on the 30th anniversary of metabolic engineering (2021)].

Metabolic engineering is the use of recombinant DNA technology, synthetic biology and genome editing to modify the cellular networks including metabolic, gene regulatory, and signaling networks of an organism. It can achieve the desirable goals such as enhanced production of metabolites, and improve the capability of biomanufacturing pharmaceuticals, biofuels and biochemicals as well as other biotechnology products. In order to comprehend the status of metabolic engineering in past 30 years, we published this special issue to review the progress and trends of metabolic engineering from the four aspects of overall development, key technologies, host engineering and product engineering, respectively, for laying the foundation for the further development of metabolic engineering.