The purpose of the Web and Mobile Security chapter is to provide an overview of security mechanisms, attacks and defences in modern web and mobile ecosystems. Web and mobile security have become the primary means through which many users interact with the Internet and computing systems. Hence, their impact on overall information security is significant due to the sheer prevalence of web and mobile applications (apps). Covering both web and mobile security, this Knowledge Area emphasises the intersection of their security mechanisms, vulnerabilities and mitigations.  We speak with CyBOK Web and Mobile Security author Sascha Fahl for an introductory overview of the topic.