The central dogma of molecular biology indicates that genetic information from DNA is transmitted to RNA, and then translated into proteins that play various roles during all physiological and pathological processes. However, most of the proteins have to make small chemical changes on their amino acid chains, so-called post-translational modifications, before they start to work. The collection of four articles in this issue presents timely developments in the area of protein modifications, ranging from how proteins carry out their biological functions based on protein modifications to what are molecular mechanisms of protein modifications.