The nematode Caenorhabditis elegans is an excellent experimental system for studying how cell division and differentiation events are orchestrated in the context of a developing animal. A set of master regulatory genes, so calle ‘heterochronic genes’, have been identified in C. elegans whose activity changes as the worm progresses through larval development. The various heterochronic genes encode transcription factors, microRNAs, RNA binding proteins, and other proteins and noncoding RNAs that comprise a developmentally dynamic regulatory network that controls the timing of cell fate transitions throughout the animal. Many of the C. elegans heterochronic genes, and in some cases the regulatory interactions amongst them, are conserved in mammals, including humans. Mutations in C. elegans heterochronic genes cause stage-specific developmental events to be expressed with incorrect timing. We are particularly intrigued by the robustness with which this network normally operates, since developmental events occur with precise and invariant timing in the wild type, regardless of environmental and physiological stresses experienced by the free-living larva. By contrast, the developmental timing phenotypes of heterochronic mutants are often dramatically modified by those same everyday stresses, indicating roles for the corresponding genes in conferring developmental robustness. I will report on recent findings from our explorations of the regulatory mechanisms underlying the robust control of developmental timing by heterochronic genes.