In today’s world, video streaming accounts for a significant share of Internet traffic. Internet Service Providers (ISPs) strive to provide these services while ensuring the best possible Quality of Experience (QoE) for users. One of the biggest challenges for ISPs is that, unlike content providers who can directly access users’ QoE metrics, they can only derive them from network measurements such as throughput, latency and packet loss. This limitation is mainly due to end-to-end encryption, which limits the possibility of deep packet inspection, by enhancing user privacy while limiting insight into application-level metrics. The goal of this thesis is to develop methods that allow ISPs to accurately estimate user QoE relying on passive network traffic measurements that can be collected without breaking end-to-end encryption.