Astronomical threats for the earth are numerous, but fortunately the most dangerous ones that can cause an extinction happens very very seldom. Even today, it is also possible to find some traces of impacts from asteroids (sometimes even comets) on the ground, such as impact craters caused by impacts of these minor bodies of the solar system. This talk is devoted to the properties of the Near-Earth Objects (NEOs), such as structure , composition , physical parameters and shape that may have close encounters (but even impacts) with terrestrial planets like Venus, Earth and Mars. Astronomers can measure these properties and determine well them. Moreover, future and past close encounters between the Earth and small bodies and their risk of impact will be discussed .