After the Great Sumatra Earthquake and the consequent Indian Ocean Tsunami scientific community puts their attention to alternative methods in ocean monitoring to improve the response of the tsunami warning systems. Improvement of classic techniques, as the seismic source estimation (e.g., Ammon et al., 2006) and densification of number of buoys over the oceans (Gonzalez et al., 2005), was supported by a new effort in remote sensing: nominally the space altimetry observation of the tsunami in the open sea (Okal et al., 1999; Smith et al., 2005) and the tsunami detection by ionospheric monitoring (e.g., Occhipinti et al., 2006). Today the recent tsunamis declare, one times more, the importance to go forward in this direction. The indirect tsunami observation by ionospheric sounding is based on the idea anticipated in the past by Hines (1972) and Peltier & Hines (1976) that tsunamis produce internal gravity waves (IGWs) in the overlooking atmosphere. During the upward propagation the IGWs are strongly amplified by the effect of the decrease of the density. The interaction of IGWs with the plasma at the ionospheric height produces strongly variation in the plasma velocity and plasma density observable by ionospheric sounding (Figure 1). This chapter i) resumes the moderne debate based on the Sumatra event (2004) about the tsunami detection by ionospheric sounding to demonstrate the hypothesis anticipated by Peltier & Hines (1976), and identifies the technics that proved and validated it, nominally altimeters and GPS. ii) Supports, with the recent theoretical works, the coupling between the ocean, the neutral atmosphere and the ionospheric plasma during the tsunami propagation and explores, based on the numerical modeling, the remote sensing possibility with additional techniques as the over the horizon radar (OTH-R). iii) Presents the ionospheric observations of the recents tsunamis to prove the systematic detection capability; nominally we review the following tsunamigenic earthquakes: 12 September, 2007, in Sumatra; the 14 November, 2007, in Chile; the 29 September, 2009, in Samoa; and the recent Tohoku-Oki (Japan) earthquake on 11 Mars 2011. We anticipate here that this last event also allow to prove that the signature of tsunami in the ionosphere can be also detected by optical camera via the airglow. It finally concludes discussing the role of ionospheric sounding and remote sensing in the modern evolution of tsunami detection and warning systems.