Posttranslational modifications (PTMs) are biochemical modifications that occur after protein synthesis, which can affect a protein's stability, activity, and localization. There are several synonyms for the term posttranslationally, including posttranslational modification, PTM, posttranslational regulation, and posttranslational processing. Protein regulation through PTMs is critical for physiological processes that underlie cellular function, including signal transduction, transcriptional and translational regulation, and cell cycle control. Disruptions in PTM processes have been implicated in a variety of diseases and disorders, including cancer, diabetes, and neurodegenerative diseases. Understanding the range and function of PTMs and their wider significance in biology will continue to be an important area of research moving forward.