Online user tracking is a widely used marketing tool in e-business, even though it is often neglected in the related literature. In this chapter, the authors provide an exhaustive survey of tracking-related identification techniques, which are often applied against the will and preferences of the users of the Web, and therefore violate their privacy one way or another. After discussing the motivations behind the information-collecting activities targeting Web users (i.e., profiling), and the nature of the information that can be collected by various means, the authors enumerate the most important techniques of the three main groups of tracking, namely storage-based tracking, history stealing, and fingerprinting. The focus of the chapter is on the last, as this is the field where both the techniques intended to protect users and the current legislation are lagging behind the state-of-the-art technology; nevertheless, the authors also discuss conceivable defenses, and provide a taxonomy of tracking techniques, which, to the authors’ knowledge, is the first of its kind in the literature. At the end of the chapter, the authors attempt to draw the attention of the research community of this field to new tracking methods.