This chapter highlights the importance of symmetric cryptographic primitives for providing security in wireless sensor networks. We outline the basic goals and primitives and give a comprehensive overview in regard to modes of operation. We also provide an extensive survey of the implementation options of the Advanced Encryption Standard (AES): In software on processors of different word size, in hardware with different optimization goals, as well as in a hardware/software co-design approach with cryptographic instruction set extensions. An overview of state-of-the-art cryptographic support in today's WSN products concludes this chapter.