The polycomb repressive complexes 2 (PRC2) complex catalyzes tri-methylation of histone H3 lysine 27 (H3K27),a repressive chromatin marker associated with gene silencing.Overexpression and mutations of PRC2 are found in a wide variety of cancers,making the catalytic activity of PRC2 an important target of cancer therapy.This review highlights recent structural breakthroughs of the human PRC2 complex bound to the H3K27 peptide and a small molecule inhibitor,which provide critically needed insight into PRC2-targeted drug discovery.