Post-translational modification of proteins, or what occurs after a protein has been synthesized by the cell, are now known to play a fundamental role in regulating the activity, location and function of a wide range of proteins. In plant cells work on different types of post-translational modifications has progressed largely along independent lines. This book brings research workers together to allow an exchange of ideas, and reflects a diversity of interest while also revealing common ground. An introductory chapter reviewing recent progress in the field is followed by reviews of protein phosphorylation in bacteria and animals, which provide a useful perspective on this subject in plants. Consideration is then given to plant protein kinases and the processes they control. Acylation and glycosylation, and their functions in protein targeting and folding are reviewed, along with the roles of glycoproteins in plant development and of ubiquitination in plant senescence.