Symmetric cryptology is one of the two main branches of cryptology. Its applications are essential and vital in the Information Age, due to the efficiency of its constructions.The scope of this book in two volumes is two-fold. First, it presents the most important ideas that have been used in the design of symmetric primitives, their inner components and their most relevant constructions. Second, it describes and provides insights on the most popular cryptanalysis and proof techniques for analyzing the security of the above algorithms. A selected number of future directions, such as post-quantum security or design of ciphers for modern needs and particular applications, are also discussed.We believe that the two volumes of this work will be of interest to researchers, to master’s and PhD students studying or working in the field of cryptography, as well as to all professionals working in the field of cybersecurity.