This chapter reviews the major approaches to the prediction of instability in superplastic forming. Theoretical and numerical approaches are treated. Key aspects include the effects of microstructure and the identification of an appropriate constitutive equation set. It is argued that the development of an easy-to-visualise superplastic forming limit diagram (SPFLD) concept is attractive as a vehicle to facilitate more widespread use of the superplastic forming (SPF) process, which is a key challenge to the technology. A case study on failure prediction for two titanium alloys is used for illustrative and comparative purposes with respect to a number of the key predictive techniques.