This book should be of interest to people who seek a fundamental understanding of the physical processes that lead to ionospheric scintillation, and the impact of ionospheric scintillation on the day-to-day communication processes. Ionospheric scintillation is a phenomenon that significantly affects the reliability and accuracy of satellite communication and navigation systems by degrading their signals. GPS systems are particularly affected in the equatorial region. In order to develop GPS receivers that are resistant to scintillation, as well as to strengthen the integrity and robustness of GPS, a thorough understanding of the characteristics and dynamics of ionospheric irregularities is crucial. In response to this need, this book presents detailed properties of ionospheric scintillation and its source mechanisms which occur during the day and at night. The results are discussed in terms of plasma irregularities and their formation processes during the day and at night in the equatorial region.