Systematic exploration of thermodynamic stability of coacervates established phase diagrams as a function of chain length, mixing ratio, pH or salt concentration. The general idea seems to be to use experimental setups with minimal number of welldefined components, such that their properties can be varied systematically. Other works, focusing for instance on the thermodynamics of the complex formation, visco-elasticity or interfacial properties, show that the coacervate phase behavior is universal to a high degree. Concurrently, theoretical approaches such as scaling (blob) arguments, mean-field and liquid-state theories, field-theoretic calculations or transfer-matrix formalism, have identified the key actors: charge correlations, counterion condensation or chain connectivity. Additionally, it has been shown, that specific chemistry of the polymer, counterions or solvent can strongly affect the stability and composition of the complexes. Nevertheless, the agreement between the experiment and theory remained mostly qualitative. While the experimental results reflect on both generic physical and specific chemical effects, the theories can systematically describe typically only the former effect, whereas the latter often enters the calculations in the form of phenomenological material constants, which are hard to evaluate or predict from theory. To enable further progress, it seems necessary to disentangle the universal and system-specific effects and to understand how they both contribute to the net result.