Since Sputnik 1 was launched in 1957, humankind has launched thousands of satellites. Many old, worn-out spacecraft, as well as the upper stages of rockets, remain in orbit around the earth – part of what is known as “space junk” or “space debris.” The amount of space junk continues to grow every year – more than 17,000 pieces of debris 10 cm in diameter or larger have been identified. These pieces travel at extremely high speeds, and objects only a few centimeters across can cause devastating damage to spacecraft upon impact, so countermeasures are urgently needed. This special feature presents some of the efforts that are being made to combat the problem of space debris.