Associative liquid–liquid phase separation (LLPS) is an active research topic in the fields of soft matter, colloid chemistry, food science, and cell biology. LLPS is a dynamic assembly process that leads to the formation of micrometer-sized droplets, known as complex coacervates. These droplets can progressively coalesce, leading to macroscopic phase separation and the formation of a continuous dense phase of coacervates. This presentation will primarily focus on heteroprotein complex coacervation (HPCC) that occurs between oppositely charged protein mixtures. First, the coacervation mechanism will be discussed with a special focus on the formation dynamics, main driving forces, and physical and chemical characteristics of the coacervates. Next, the rheological properties of HPCC, based on a model system consisting of positively charged lactoferrin (LF) and negatively charged β-lactoglobulin (βLG), will be discussed. The influence of a slight variation of physicochemical parameters such as pH, ionic strength, and temperature on the rheological properties will be examined. The similarities and differences of HPPC rheological properties with protein-polysaccharide or synthetic polymer systems will be highlighted. Lastly, the potential applications of HPCC within the food industry will be discussed, including its roles as an encapsulation vehicle, viscosity enhancer, and stabilizing agent.