Developmental phase switches and identity changes need global changes in gene expression patterns.Genome-wide chromatin immunoprecipitation approaches have provided insights into the transcriptional networks and topology of the networks that underlie phase changes and identity specification.Phase switches involve suppression of the preceding developmental programme by negative feedback regulation and activation of the next developmental programme by positive (autoregulatory) regulation mechanisms.Combinatorial interaction among transcription factors determines regulatory specificity and defines the set of target genes.Key regulators are transcription factors and chromatin modifiersThese key regulators form protein complexes and the transcription factors may recruit the chromatin modifiers to specific loci.