In deployments of biometrics, secure storage of biometric information is necessary in order to protect the users’ privacy. Within this context, biometric template protection (BTP) mechanisms are designed to meet key requirements of biometric information protection, enabling privacy-preserving storage and comparison of biometric data. Biometric cryptosystems, a subset of biometric template protection methods, are explored in this chapter, which presents a general introduction to their principles and applications. Based on a categorisation of existing schemes, popular cryptographic primitives, i.e. the fuzzy commitment and fuzzy vault scheme, are described in detail along with relevant works applying them to different biometric characteristics. Error correction coding techniques that are frequently employed in biometric cryptosystems are explained. In addition, the concept of feature-type transformation in order to make biometric feature vectors compatible with biometric cryptosystems is discussed. Subsequently, implementations based on different types of biometric cryptosystems are presented and obtained results are reported. Finally, open challenges are discussed.