This chapter examines the arms race between corporate surveillance and the countermeasures that allow users to defend themselves against advertising, tracking, and profiling. The chapter first explains ad blockers as the most common countermeasure, and shows how the industry is using anti-ad blockers to block ad blocker users. The chapter then discusses specialized blockers for tracking and fingerprinting, as well as countermeasures based on obfuscation and tools that aim to increase user awareness, before closing with a discussion of countermeasures for mobile devices and applications.