In this chapter, we discuss how terrorists can use the Internet as a source of information to plan for terrorist attacks. Online anonymity services such as virtual private network (VPN) are discussed, along with advantages and disadvantages of using these services. We also discuss online bomb-making instructions and highlight ways in which these can be used to the advantage of law enforcement. Finally, the use of the Internet as a reconnaissance tool for target selection is discussed, with descriptions of current and past research in this field to identify key information that is available to terrorists, and how this information can be manipulated to reduce the likelihood or severity of a terrorist attack.