Societal dependence on Information and Communication Technology (ICT) over the past two decades has brought with it an increased vulnerability to a large variety of cyber-attacks. One such attack is a Distributed Denial-of-Service (DDoS) attack which harnesses the power of a larger number of compromised and geographically distributed computers and other networked machines to attack information-providing services, often resulting in significant downtime and thereby causing a denial-of-service to legitimate clients. The size, frequency, and sophistication of such attacks have exponentially risen over the past decade. In order to develop a better understanding of these attacks and defense system against this ever-growing threat, it is essential to understand their modus operandi, latest trends and other most widely-used tactics. Consequently, the study of DDoS attacks and techniques to accurately and reliably detect and mitigate their impact is an important area of research. This chapter largely focuses on the current landscape of DDoS attack detection and defense mechanisms and provides detailed information about the latest modus operandi of various network and application layer DDoS attacks, and presents an extended taxonomy to accommodate the novel attack types. In addition, it provides directions for future research in DDoS attack detection and mitigation.