The use of electronic technologies in government services has played a significant role in making citizens’ lives more convenient. Even though the transition to digital governance has great advantages for the quality of government services it may be accompanied with many security threats. One of the major threats and hardest security problems e-Government faces are the Denial of Service (DoS) attacks. DoS attacks have already taken some of the most popular e-government sites off-line for several hours causing enormous losses and repair costs. In this chapter, important incidents of DoS attacks and results from surveys that indicate the seriousness of the problem are presented. In order to limit the problem of DoS attacks in government organisations we also present a list of best practices that can be used to combat the problem together with a classification of attacks and defense mechanisms.