Fundamental mechanisms that regulate chromatin assembly and transcription have been elucidated recently using genetics and highly defined biochemical systems. Once DNA is packaged into chromatin, its function is controlled by the ordered recruitment of diverse enzymatic complexes that structurally remodel or chemically modify nucleosomes. Recent studies provide insight into the functional selectivity of chromatin-remodeling and -modifying complexes and how they act in specific combinations to regulate individual genes and cellular pathways.