Notch signaling is important for development in Caenorhabditis elegans and the REF-1 family pro-teins, a set of the bHLH transcription factors, are the first targets of Notch signaling. Little is known about the molecular mechanisms employed by the REF-1 family to regulate development. In this project, I iden-tified novel targets of three REF-1 family proteins, HLH-25/HLH-28/HLH-29, and determined which target genes are activated and which are repressed by the REF-1 proteins. These targets were identified by gene expression microarray and were functionally categorized by Gene Oncology analysis. A systems biology approach was performed to identify networks associated with those targets. In addition to the mo-lecular genetics studies, I identified and better characterized the range of phenotypes induced by muta-tions in ref-1 family genes.