Coacervates are micron-sized liquid droplets, formed by liquid-liquid phase separation directed by attractive and segregative forces, that have attracted considerable interest as protocells. These droplets are used as in-vitro models for membraneless organelles in cells, which store and protect cellular material from the environment. Their ability to encapsulate reactions, preserve the products against environmental fluctuations, and possibly allow for the emergence of more complex molecular structures all suggest that they may have played a role in the formation of cells at the origins of life. A key role in protocell models, as well as in modern-day biological processes, is played by the interactions of coacervates with the surrounding environment and their ability to exchange molecules with the dilute phase.