This chapter examines the conditions under which scintillations occur in the natural ionosphere and describes the extent to which scintillations can disrupt the performance of the space-based communications and navigation systems, as well as both ground- and space-based radar applications. It considers potential strategies to mitigate ionospheric impacts, briefly explores the use of these technologies as sensors to monitor the state of the ionosphere, and detects the conditions in which system performance may be compromised by space weather. The chapter begins with a brief overview of the fundamental propagation theory. The degradation experienced by different types of radio frequency applications is described in generic terms. The chapter provides better understanding of how space weather impacts global navigation satellite system, at least on a qualitative level. Impacts caused by space weather may be attributed to other factors, such as equipment malfunctions or electromagnetic interference.