In this chapter we discuss Distributed Denial of Service (DDoS) attacks in networks such as the Internet, which have become significantly prevalent over the recent years. We explain how DDoS attacks are performed and consider the ideal solution characteristics for defending against the DDoS attacks in the Internet. Then we present different research directions and thoroughly analyse some of the important techniques that have been recently proposed. Our analysis confirms that none of the proposed techniques can efficiently and completely counteract the DDoS attacks. Furthermore, as networks become more complex, they become even more vulnerable to DoS attacks when some of the proposed techniques are deployed in the Internet. The gap between the tools that can generate DDoS attacks and the tools that can detect or prevent DDoS attacks continues to increase. Finally, we briefly outline some best practices that the users are urged to follow to minimise the DoS attacks in the Internet.