A Liquid–liquid phase condensate (LLPC) results from de-mixing into two distinct liquid phases, with different concentrations of macromolecular solutes. This process is thermodynamically-driven and reversible. Such phase separation can form a coacervate as an aqueous phase enriched in certain macromolecules (proteins, RNA, DNA) due to favorable multivalent interactions despite the reduction in entropy. The physics of LLPCs is often used by X-ray crystallographers to obtain super saturation of macromolecules in phase separated droplets to nucleate crystallization. In cells such phase separations can lead to the spontaneous formation of a meta-stable dense phase enriched in macromolecules that is in thermodynamic equilibrium with a dilute phase. This provides the cell biology with the potential for efficient meta-stable compartmentalization without the need for a membrane that can be controlled by small changes such as post-translational modifications. Such LLPCs may have acted in the origin of life and been preserved in modern cells for functions requiring orchestration of pathways such as DNA repair that could otherwise be disrupted by stochastic interactions of diverse and competing macromolecules and even intermediates during complex biological pathways. Disruption of LLPCs may therefore be a factor in development, aging, genome instability, cancer, pathogenesis, and immune responses. Can you suggest effective ways I might measure LLPCs and determine their potential functional roles?