Many of the applications of classical coding techniques can be found at the physical layer of contemporary communication systems. However, coding ideas have recently found their way into networking research, most strikingly in the form of algebraic codes for networks. The existing body of work on network coding ranges from determinations of the fundamental limits of communication networks to the development of efficient, robust, and secure network-coding protocols. This chapter provides an overview of the field of network coding with particular emphasis on how the unique characteristics of network codes can be exploited to achieve high levels of security with manageable complexity. We survey network-coding vulnerabilities and attacks, and compare them with those of state-of-the-art routing algorithms. Some emphasis will be placed on active attacks, which can lead to severe degradation of network-coded information flows. Then, we show how to leverage the intrinsic properties of network coding for information security and secret-key distribution, in particular how to exploit the fact that nodes observe algebraic combinations of packets instead of the data packets themselves. Although the prevalent design methodology for network protocols views security as something of an add-on to be included after the main communication tasks have been addressed, we shall contend that the special characteristics of network coding warrant a more comprehensive approach, namely one that gives equal importance to security concerns. The commonalities with code constructions for physical-layer security will be highlighted and further investigated.