For organic and hybrid organic-inorganic crystals, molecular orientational disorder, which can be considered a form of configurational disorder, is common and has important implications for phase stability. In cases where local order is significant, methods taking such effects into account are needed. Degrees of freedom related to electronic and magnetic excitations may also be important for assessing phase stability in certain cases. For metals, there is always an entropic contribution from electronic excitations near the Fermi level. This term is typically small, but must be included when phase competition happens between metallic and insulating phases. Furthermore, effects of electronic entropy are also present in mixed valence compounds, in which it takes a role similar to configurational entropy, but for different charge states of the same element. This has been shown to be of importance in the ionic conductor Li x FePO 4 . Another complex entropic stabilisation mechanism is related to ionic conductivity. For superionic conductors, this is considered a partial melting of one sublattice, and analogously to the increased entropy of a liquid, there must be an entropic stabilisation associated with the superionic state. For example, the oxygen sublattice melting in Bi 2 O 3 , La 2 Mo 2 O 9 and Bi 4 V 2 O 11 . The entropy of the disordered system can be estimated from simple considerations based on available interstitial sites, or more elaborate methods based on thermodynamic integration can be applied. As ionic conductors are important for applications in batteries and fuel cells, it will be advantageous if simple but accurate models for prediction of their stability can be established.