Abstract
Polycomb group (PcG) protein complexes dynamically define cellular identity through the regulation of key developmental genes. Important advances in the PcG field have come from genome-wide mapping studies in a variety of tissues and cell types that have analyzed PcG protein complexes, their associated histone marks and putative mechanisms of PcG protein recruitment. We review how these analyses have contributed to our understanding of PcG protein complex targeting to chromatin and consider the importance of diverse PcG protein complex composition for gene regulation. Finally, we focus on the dynamics of PcG protein complex action during cell fate transitions and on the implications of histone modifications for cell lineage commitment.