Complex molecular systems, in which large numbers of molecules react and interact with one another to give rise to emergent properties and behaviours, are present in every aspect of the world around us. Nature provides spectacular examples of molecularly-fuelled motion, chemical communication, quorum sensing, adaptive materials, oscillating reactions, and self-replicating systems, among others. The aim of systems chemistry is to understand the emergence of these properties from complex reaction networks, and to incorporate these networks into synthetic materials.

In living systems, complex reaction networks are organized into dynamic compartments, which sets the stage for the potential of this approach. Coacervation is a versatile way to create compartments with distinct chemical properties, through liquid–liquid phase separation. The size of these compartments ranges from the nanoscale to the mesoscale. They could act as organelles in a synthetic cell, be used as building blocks for smart materials, as catalysts, or to deliver cargo. They may also have played a role as protocells during the emergence of cellular life. Coacervates can bring subsets of molecules together, modulate their activity, and direct their interactions, thereby altering chemical reactions and assemblies. In return, chemistry can control the coacervation process and tune the chemical properties of coacervates, forging an intimate bond between coacervation and systems chemistry.