The International Space Station (ISS) is a large spacecraft that orbits Earth at an average altitude of 400 kilometers (250 miles). It serves as a unique laboratory for scientific research in a microgravity environment, enabling experiments in fields like biology, physics, and astronomy that aren't possible on Earth. The ISS is a joint project between space agencies such as NASA (USA), Roscosmos (Russia), ESA (Europe), JAXA (Japan), and CSA (Canada).