Embodiments of systems and methods for flexible Channel State Information (CSI) feedback in a cellular communications network are disclosed. In some embodiments, a base station configures a wireless device with a set of CSI-RS resources, dynamically configures a CSI-RS resource from the set of CSI-RS resources for measurement, and receives a CSI report from the wireless device determined from the CSI-RS resource dynamically configured for measurement. In this manner, the base station is enabled to dynamically configure and re-configure the CSI-RS resource(s) for measurement by the wireless device, which in turn provides flexible CSI feedback that is particularly well-suited for embodiments in which the base station transmits beamformed CSI-RS.