Space starts at a height of 100 km above the Earth's surface. Space is not empty. In addition to the electromagnetic radiation from the Sun, there are a lot of additional components. The main contributions come from: the Earth's magnetic field, the upper residual atmosphere, plasma, UV- and X-rays, particle radiation (electrons, protons and heavy ions) from the Sun and other galactic sources, dust and meteoroids, asteroids and comets, as well as space debris. These components of the space environment affect all objects in space and sometimes also the Earth. Some examples are the auroras, electrostatic discharges on satellites, the radiation risk for astronauts and electronic components of satellites, disruptions of communication and navigation, impacts of meteoroids and space debris on satellites, meteors and near-Earth asteroids. The work in and around this area deals with measurements and modulations of the space environment and their consequences.