Large-scale gene synthesis in tiny droplets Gene synthesis technology is important for functional characterization of DNA sequences and for the development of synthetic biology. However, current methods are limited by their low scalability and high cost. Plesa et al. developed a gene synthesis method, DropSynth, which uses barcoded beads to concentrate oligos and subsequently assemble them into synthetic genes within picoliter emulsion droplets. DropSynth allows generation of large libraries of thousands of genes and functional testing of all possible mutations of a particular sequence. Science , this issue p. 343