Giant planets are the most prominent representative bodies not only in the solar system but also in other extrasolar systems. The origin of the Jovian planets and the icy moons are inseparable and thus their origin, internal structure, composition, etc. will be comprehensively discussed. In front of the future mission Era, we'd like to promote the study of Jovian planets and their satellites. Also, progress in developing a solar sail mission to observe Jupiter system and Trojan asteroids will be discussed.