Digital watermarking studies have always been driven by the improvement of robustness. Most of articles of this field deal with this criterion, presenting more and more impressive experimental assessments. Some key events in this quest are the use of spread spectrum, the invention of resynchronization schemes, the discovery of side information channel, and the formulation of the embedding and attacking strategies as a game. On the contrary, security received little attention in the watermarking community. This chapter presents a comprehensive overview of this recent concept. We list the typical applications which require a secure watermarking technique. For each context, a threat analysis is purposed. This presentation allows us to illustrate all the certainties the community has on the subject, browsing all key papers. The end of the paper is devoted to what remains not clear, intuitions and future trends.