In the past fifty-five years, the space around the Earth has gone from a virtually debris-free environment to a zone cluttered with man-made objects that threaten launches, active satellites, and the International Space Station (ISS). NASA reports that as of 2013, more than 21,000 pieces at least the size of a softball were being tracked, and an estimated 500,000 pieces at least the size of a marble are thought to exist. More than 100 million even smaller objects, ranging down to the size of a tiny fleck of paint, are too small to detect or track. Active satellites, numbering about 1,100, comprise about 6 percent of Earth-orbiting objects; the rest is junk, commonly called space debris. This paper examines what space debris consists of, where it came from, and what problems it is causing.