Methylation at the fifth position of the cytosine base (5mC) is a critical DNA modification with important functions in gene silencing, genome imprinting, and suppression of transposable elements in eukaryotes. Biochemically, DNA methylation is dynamically regulated by three critical processes: the de novo establishment of DNA methylation, the maintenance of DNA methylation by preexisting methylation patterns, and the removal of DNA methylation. In plants, DNA methylation is very complex with unique features. In past decades, a series of biochemical and structural studies, especially empowered by the recent breakthroughs of high-resolution cryogenic electron microscopy, have helped uncover the molecular mechanisms underlying the establishment, maintenance, and removal of DNA methylation in plants. This review summarizes recent research advances in these three aspects of DNA methylation and lays out a molecular view of plant DNA methylation from biochemical and structural perspectives.