The growing use of Internet service in the past few years have facilitated an increase in the denial of service (DoS) attacks. Despite the best preventative measures, DoS attacks have been successfully carried out against high-prole organizations and enterprises, including those that took down Chase, BOA, PNC and other major US banks in September 2009, which reveal the vulnerability of even well equipped networks. These widespread attacks have resulted in significant loss of service, money, and reputation for organizations, calling for a practical and ecient solution to DoS attack detection and mitigation. DoS attack detection and mitigation strengthens the robustness and security of network or computer system, by monitoring system activities for suspicious behaviors or policy violations, providing forensic information about the attack, and taking defensive measures to reduce the impact on the system. In general, attacks can be detected by (1) matching observed network trac with patterns of known attacks; (2) looking for deviation of trac behavior from the established prole; and (3) training a classier from labeled dataset of attacks to classify incoming trac. Once an attack is identied, the suspicious trac can be blocked or rate limited. In this presentation, we present a taxonomy of DoS attack detection and mitigation techniques, followed by a description of four representative systems (Snort, PHAD, MADAM, and MULTOPS). We conclude with a discussion of their pros/cons as well as challenges for future work.