Which of the following data protection milestones is a treaty among member states of the Council of Europe?

Convention 108 is indeed a key data protection milestone and is significant in the landscape of privacy legislation, particularly in Europe. It was established by the Council of Europe and is formally known as the "Convention for the Protection of Individuals with regard to Automatic Processing of Personal Data." This treaty was first opened for signature in 1981 and serves as the first legally binding international instrument that specifically addresses privacy and data protection principles.

The significance of Convention 108 lies in its foundational role in the development of data protection laws across Europe and beyond. It promotes the idea that individuals have the right to privacy and outlines principles such as the legitimacy of data processing, the purpose limitation of data collection, and the rights of individuals regarding their personal data. Additionally, it established a framework that encourages cooperation among member states to ensure that their national policies align with privacy principles.

In contrast, the other options provided do not represent a treaty among member states of the Council of Europe. The Data Retention Directive and the e-Privacy Directive are legislative acts of the European Union that relate to data retention and privacy in electronic communications but are not treaties. The Charter of Fundamental Rights, while significant in the EU context and encompassing fundamental rights, serves as a declaration of rights rather than a binding treaty