Denial-of-service (DoS) attacks are among the least understood of IT security threats. From a technical standpoint, launching a DoS attack is easy. Protecting against these attacks is a challenge. The key is not to react to a DoS attack, but to act before such an attack even occurs. This booklet, or “blog book”, collects a group of blog posts that pursue a common goal: to increase our understanding of DoS attacks and learn how to protect against them.