Ionospheric irregularities are the source of scintillation, defined as rapid random fluctuations in the amplitude and phase of radio signals that adversely affect transionospheric communication and navigation systems. Scintillations are the most severe at magnetic low- and high-latitudes; however, recent reports have demonstrated robust scintillation in midlatitude regions, as well. These irregularities with characteristic scales ranging from 100s of meters to 10s ok km in conjunction with larger-scale density perturbations impact radio and radar systems. The generation mechanisms producing these ionospheric density irregularities are controlled by the background density, electric fields, plasma drift, neutral winds, and particle precipitation. Understanding the state of the system controlling the instability onset, growth, and saturation is paramount for forecasting and mitigation strategies. In this session, we invite both modeling and observational studies pertinent to advancing our understanding of the role of various processes for the generation of ionospheric irregularities and their propagation impacts.