The nucleolus is a liquid-like cellular organelle where protein factories called ribosomes are assembled. Researchers knew of three distinct compartments within the nucleolus, but how these compartments function to drive ribosome assembly was unclear. A study from St. Jude Children's Research Hospital, published today in Molecular Cell, reveals that smaller subcompartments containing ribosome building blocks and assembly proteins spontaneously form to finish the final steps of ribosome assembly. This reveals unprecedented levels of organization behind the process and may offer insight into diseases associated with increased ribosome production, such as cancer.