The 336–year–old synchronization observations of Christiaan Huygens are re–examined in modern experiments. A simple model of synchronization is proposed.

Engineering cell population behavior: Attaining the full promise of synthetic biology will require designing population-level behaviors of multiple interacting cell types. As a start, Chen et al. engineered two strains of the bacterium Escherichia coli to produce signaling molecules that regulate transcription in the complementary strain (see the Perspective by Teague and Weiss). The signaling circuit was successfully designed to produce feedback loops that produce synchronous oscillations in transcription between the two strains. A mathematical model helped determine how to modulate the oscillations and control their robustness to perturbations. Science , this issue p. 986 ; see also p. 924