Biomolecular condensates are cellular compartments that concentrate proteins and nucleic acids without an encapsulating membrane. They act in processes across the biological spectrum, from RNA metabolism to signaling and gene regulation. Macromolecular phase separation, akin to the separation of oil from water, has emerged over the past several years as a key organizer both of condensates, and of micron-scale cell organization in general. This conference brings together for the first time at Keystone Symposia scientists studying biomolecular condensates and macromolecular phase separation from varied perspectives and across scales of length and time. Theory, biophysics, biochemistry, cell biology and developmental biology will be joined together to address central questions in the field—how is molecular specificity in condensates achieved, how are the material properties and spatial structure of condensates controlled, how do composition and physical properties lead to emergent functions, how does aberrant formation of condensates lead to diseases such as neurodegeneration and cancer? By bringing together leading scientists from diverse areas impacted by phase separation, we hope to clarify the current state of knowledge in this exciting new field and identify important future directions.