This chapter covers the different facets of security as applicable to Service-Oriented Architecture (SOA) implementations. First, it examines the security equirements in SOA implementations, highlighting the differences as compared to the requirements of generic online systems. Later, it discusses the different solution mechanisms to address these requirements in SOA implementations. In the context of Web services, the predominant SOA implementation standards have a crucial role to play. This chapter critically examines the crucial Web services security standards in different stages of adoption and standardization. Later, this chapter examines the present-day common nonstandard security mechanisms of SOA implementations. Towards the end, it discusses the future trends in security for SOA implementations with special bearing on the role of standards. The authors believe that the pragmatic analysis of the multiple facets of security in SOA implementations provided here will serve as a guide for SOA security practitioners.