This paper gives a classification of intentional and unintentional threats, such as interference, jamming and spoofing, and discusses some of the recent trends concerning techniques for their detection and mitigation. Despite the fact that these phenomena have been studied since the early stages of Global Positioning System (GPS), they were mainly addressed for military applications of Global Navigation Satellite Systems (GNSS). However, a wide range of recent civil applications related to user’s safety or featuring financial implications would be deeply affected by interfering or spoofing signals intentionally created. For such a reason, added value processing algorithms are being studied and designed, in order to improve accuracy and robustness of the receiver and to assure the reliability of the estimated position and time solution.