Chemical biology approaches are a powerful means to functionally characterize epigenetic regulators such as histone modifying enzymes. We outline experimental protocols and best practices for the cellular characterization and use of “chemical probes” that selectively inhibit protein methyltransferases, many of which methylate histones to regulate heritable gene expression patterns. We describe biomarker assays to validate the probes in specific cellular systems, and provide guidelines for their use in functional characterization of methyltransferases including detailed protocols, examples, and controls. Together these techniques enable precision manipulation of cellular epigenomes and the exploration of the therapeutic potential of epigenetic targets in human disease.