\chapter{Preliminaries} \label{ch:prel} In this chapter, we introduce some relevant terminology and background knowledge around the problem of continuous publishing of sensitive data sets. First, we categorize data as we view them in the context of continuous data publishing. Second, we define data privacy, we list the kinds of attacks that have been identified in the literature, as well as the desired privacy levels that can be achieved, and the basic privacy operations that are applied to achieve data privacy. Third, we provide a brief overview of the seminal works on privacy-preserving data publishing, used also in continuous data publishing, fundamental in the domain and important for the understanding of the rest of the chapter. \input{preliminaries/data} \input{preliminaries/privacy} \input{preliminaries/summary}