This chapter examines the balanced relationship between the advantages of biometric systems and the disadvantage of immutable biometric characteristics. Potential attack points in biometric systems are discussed, and examples of real-life incidents in operational systems are provided, motivating the use of Biometric Template Protection (BTP) for the protection of biometric references. This chapter derives from risks in operational systems the design goals for template protection algorithms, namely non-invertibility and diversification among others. Such goals have been instrumental in the development of template protection mechanisms over the last 20 years. The chapter also reviews standardized evaluation methodologies for BTP methods and reflects on the threat models, which are applicable in evaluations of BTP mechanisms.