Following fertilisation, animal development is initially regulated by maternal factors that are present in the unfertilised egg. Developmental control then transfers to the zygotic genome, in a process known as the maternal-to-zygotic transition (MZT). Now, on p. 923, William Theurkauf and colleagues identify the RNA-binding protein Smaug as an essential regulator of MZT in Drosophila. The researchers report that Smaug, which participates in maternal mRNA destruction during MZT, is also required for other MZT-associated events, such as slowing of the cleavage divisions, cellularisation, DNA replication checkpoint activation and the initiation of zygotic transcription, including that of the miR-309cluster of microRNAs. This cluster directs the degradation of certain maternal mRNAs during MZT, indicating that Smaug mediates mRNA destruction both directly and indirectly. Furthermore, when the researchers transgenically expressed Smaug in an anterior-to-posterior gradient in the zygote, many MZT-associated events were initiated in a concentration-dependent manner. From their results, the authors propose that Smaug accumulation drives a maternal clock that controls MZT timing.