The above definition of metastability includes both materials that are thermodynamically stable at some other set of conditions (e.g. high temperature or pressure) and materials that are not thermodynamically stable at any set of equilibrium conditions, but may still be formed under certain synthesis conditions and remain kinetically stable. Thus, it is clear that for a full assessment of stability, we must go beyond metrics based on athermal energies. In this perspective, we assess the current status of the field including advances in free energy descriptions and statistical models to assess crystal stability and synthesisability.