show Abstracthide AbstractPrecise control of developmental processes is encoded in the genome in the form of gene regulatory networks (GRNs). Such multi-factorial systems are difficult to decode in vertebrates owing to their complex gene hierarchies and transient dynamic molecular interactions. Here we present a genome-wide in vivo reconstruction of the GRN underlying development of neural crest (NC), an emblematic embryonic multipotent cell population. By coupling NC-specific epigenomic and single-cell transcriptome profiling with genome/epigenome engineering in vivo, we identify multiple regulatory layers governing NC ontogeny, including NC-specific enhancers and super-enhancers, novel trans-factors and cis-signatures. Assembling the NC regulome has allowed the comprehensive reverse engineering of the NC-GRN at unprecedented resolution. Furthermore, identification and dissection of divergent upstream combinatorial regulatory codes has afforded new insights into opposing gene circuits t hat define canonical and neural NC fates. Our integrated approach, allowing dissection of cell-type-specific regulatory circuits in vivo, has broad implications for GRN discovery and investigation. Overall design: Genome-wide transcriptome profiling avian neural crest (NC) at 2 different stages of the NC ontogeny isolted from their in vivo context.