Liquid–liquid phase separation (LLPS) has emerged as a new paradigm in the fields of soft matter, colloid chemistry, food science and cell biology. Research in this area constitutes a fine example where physics and biology intertwine harmoniously. LLPS is a dynamic assembly process that leads, in solution or in vivo, to the formation of micrometer-sized droplets, which are referred as biomolecular condensates, membrane less organelles, liquid droplets or complex coacervates, depending on the scientific community concerned [1,2]. In this presentation, I focus on LLPS that occurs in binary cationic and anionic protein mixtures (heteroprotein systems, HPCC). I briefly review aspects that are of particular interest: formation dynamics; main driving forces; physical and chemical properties; functions and applications. Throughout studied binary protein systems, the route to complex coacervation involves the formation of intermediate hetero-oligomers specific for each binary system. Dimers, tetramers, or pentamers were identified (Fig. 1). While the mechanism behind the association of these primary units into building blocks and their growth to form complex coacervates remain elusive, I will present and discuss the main relevant structural and physicochemical parameters for HPCC. Finally, the challenges and future research directions in particular how HPCC can be explored in the food sector for the encapsulation and protection of bioactives or to modify the viscosity of the food matrices will be discussed.