Histones are far more than just the basic units of chromatin. Posttranslational modifications of histone tails have emerged as important regulatory mechanisms for diverse biological processes, including genome organization, gene expression, transposable element suppression, development, and environmental responses. This field is expanding rapidly with the development of new technologies and growing interest from both the basic and translational research communities. The past two decades have witnessed tremendous progress in our understanding of the complex, multilayered regulation and actions of histone modifications in plants. This review summarizes the characteristics, localization, and molecular functions of histone modifications with an emphasis on the well-studied marks in